recipe engine: extract infra-specific paths out of the engine

recipe_modules/shutil/example.expected/basic.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "\nimport os\nimport sys\nos.remove(sys.argv[1])\n",
       "bar"
     ],
-    "cwd": "[SLAVE_BUILD]",
     "name": "foo",
     "~followup_annotations": [
       "@@@STEP_LOG_LINE@python.inline@@@@",
       "@@@STEP_LOG_LINE@python.inline@import os@@@",
       "@@@STEP_LOG_LINE@python.inline@import sys@@@",
       "@@@STEP_LOG_LINE@python.inline@os.remove(sys.argv[1])@@@",
       "@@@STEP_LOG_END@python.inline@@@"
     ]
   },
   {
     "cmd": [
       "python",
       "-u",
       "\nimport json, os, sys\nif os.path.exists(sys.argv[1]) and os.path.isdir(sys.argv[1]):\n  with open(sys.argv[2], 'w') as f:\n    json.dump(os.listdir(sys.argv[1]), f)\n",
       "/fake/dir",
       "/path/to/tmp/json"
     ],
-    "cwd": "[SLAVE_BUILD]",
     "name": "listdir fake dir",
     "~followup_annotations": [
       "@@@STEP_LOG_LINE@json.output@[@@@",
       "@@@STEP_LOG_LINE@json.output@  \"file 1\", @@@",
       "@@@STEP_LOG_LINE@json.output@  \"file 2\"@@@",
       "@@@STEP_LOG_LINE@json.output@]@@@",
       "@@@STEP_LOG_END@json.output@@@",
       "@@@STEP_LOG_LINE@python.inline@@@@",
       "@@@STEP_LOG_LINE@python.inline@import json, os, sys@@@",
       "@@@STEP_LOG_LINE@python.inline@if os.path.exists(sys.argv[1]) and os.path.isdir(sys.argv[1]):@@@",
       "@@@STEP_LOG_LINE@python.inline@  with open(sys.argv[2], 'w') as f:@@@",
       "@@@STEP_LOG_LINE@python.inline@    json.dump(os.listdir(sys.argv[1]), f)@@@",
       "@@@STEP_LOG_END@python.inline@@@"
     ]
   },
   {
     "cmd": [
       "some",
       "command"
     ],
-    "cwd": "[SLAVE_BUILD]",
     "name": "manipulate file 1"
   },
   {
     "cmd": [
       "some",
       "command"
     ],
-    "cwd": "[SLAVE_BUILD]",
     "name": "manipulate file 2"
   },
   {
     "cmd": [
       "echo",
-      "[TMP_BASE]/prefix_a_tmp_1"
+      "[TMP]/prefix_a_tmp_1"
     ],
-    "cwd": "[SLAVE_BUILD]",
     "name": "print prefix_a"
   },
   {
     "cmd": [
       "echo",
-      "[TMP_BASE]/prefix_b_tmp_2"
+      "[TMP]/prefix_b_tmp_2"
     ],
-    "cwd": "[SLAVE_BUILD]",
     "name": "print prefix_b"
   },
   {
     "cmd": [
       "python",
       "-u",
       "\nimport shutil\nimport sys\nshutil.copy(sys.argv[1], sys.argv[2])\n",
       "abcde",
       "tmp_file.txt"
     ],
-    "cwd": "[SLAVE_BUILD]",
     "name": "write_simple"
   },
   {
     "cmd": [
       "python",
       "-u",
       "\nimport shutil\nimport sys\nshutil.copy(sys.argv[1], sys.argv[2])\n",
       "tmp_file.txt",
       "/path/to/tmp/"
     ],
-    "cwd": "[SLAVE_BUILD]",
     "name": "read_simple"
   },
   {
     "cmd": [
       "python",
       "-u",
       "\nimport shutil\nimport sys\nshutil.copy(sys.argv[1], sys.argv[2])\n",
       "! ~&&",
       "tmp_file.txt"
     ],
-    "cwd": "[SLAVE_BUILD]",
     "name": "write_symbols"
   },
   {
     "cmd": [
       "python",
       "-u",
       "\nimport shutil\nimport sys\nshutil.copy(sys.argv[1], sys.argv[2])\n",
       "tmp_file.txt",
       "/path/to/tmp/"
     ],
-    "cwd": "[SLAVE_BUILD]",
     "name": "read_symbols"
   },
   {
     "cmd": [
       "python",
       "-u",
       "\nimport shutil\nimport sys\nshutil.copy(sys.argv[1], sys.argv[2])\n",
       "abcde fgh",
       "tmp_file.txt"
     ],
-    "cwd": "[SLAVE_BUILD]",
     "name": "write_spaces"
   },
   {
     "cmd": [
       "python",
       "-u",
       "\nimport shutil\nimport sys\nshutil.copy(sys.argv[1], sys.argv[2])\n",
       "tmp_file.txt",
       "/path/to/tmp/"
     ],
-    "cwd": "[SLAVE_BUILD]",
     "name": "read_spaces"
   },
   {
     "cmd": [
       "python",
       "-u",
       "\nimport shutil\nimport sys\nshutil.copy(sys.argv[1], sys.argv[2])\n",
       "ab\ncd\nefg\n",
       "tmp_file.txt"
     ],
-    "cwd": "[SLAVE_BUILD]",
     "name": "write_multiline"
   },
   {
     "cmd": [
       "python",
       "-u",
       "\nimport shutil\nimport sys\nshutil.copy(sys.argv[1], sys.argv[2])\n",
       "tmp_file.txt",
       "/path/to/tmp/"
     ],
-    "cwd": "[SLAVE_BUILD]",
     "name": "read_multiline"
   },
   {
     "cmd": [
       "python",
       "-u",
       "\nimport sys, os\npath = sys.argv[1]\nmode = int(sys.argv[2])\nif not os.path.isdir(path):\n  if os.path.exists(path):\n    print \"%s exists but is not a dir\" % path\n    sys.exit(1)\n  os.makedirs(path, mode)\n",
-      "[SLAVE_BUILD]/copytree_example_tmp",
+      "[TMP]/copytree_example_tmp",
       "511"
     ],
-    "cwd": "[SLAVE_BUILD]",
     "name": "makedirs makedirs",
     "~followup_annotations": [
       "@@@STEP_LOG_LINE@python.inline@@@@",
       "@@@STEP_LOG_LINE@python.inline@import sys, os@@@",
       "@@@STEP_LOG_LINE@python.inline@path = sys.argv[1]@@@",
       "@@@STEP_LOG_LINE@python.inline@mode = int(sys.argv[2])@@@",
       "@@@STEP_LOG_LINE@python.inline@if not os.path.isdir(path):@@@",
       "@@@STEP_LOG_LINE@python.inline@  if os.path.exists(path):@@@",
       "@@@STEP_LOG_LINE@python.inline@    print \"%s exists but is not a dir\" % path@@@",
       "@@@STEP_LOG_LINE@python.inline@    sys.exit(1)@@@",
       "@@@STEP_LOG_LINE@python.inline@  os.makedirs(path, mode)@@@",
       "@@@STEP_LOG_END@python.inline@@@"
     ]
   },
   {
     "cmd": [
       "python",
       "-u",
       "\nimport shutil\nimport sys\nshutil.copy(sys.argv[1], sys.argv[2])\n",
       "some file content",
-      "[SLAVE_BUILD]/copytree_example_tmp/dummy_file"
+      "[TMP]/copytree_example_tmp/dummy_file"
     ],
-    "cwd": "[SLAVE_BUILD]",
-    "name": "write [SLAVE_BUILD]/copytree_example_tmp/dummy_file"
+    "name": "write [TMP]/copytree_example_tmp/dummy_file"
   },
   {
     "cmd": [
       "python",
       "-u",
       "\nimport shutil\nimport sys\nshutil.copytree(sys.argv[1], sys.argv[2], symlinks=bool(sys.argv[3]))\n",
-      "[SLAVE_BUILD]/copytree_example_tmp",
-      "[SLAVE_BUILD]/copytree_example_tmp2",
+      "[TMP]/copytree_example_tmp",
+      "[TMP]/copytree_example_tmp2",
       "0"
     ],
-    "cwd": "[SLAVE_BUILD]",
     "name": "copytree"
   },
   {
     "cmd": [
       "python",
       "-u",
       "\nimport shutil\nimport sys\nshutil.copy(sys.argv[1], sys.argv[2])\n",
-      "[SLAVE_BUILD]/copytree_example_tmp2/dummy_file",
+      "[TMP]/copytree_example_tmp2/dummy_file",
       "/path/to/tmp/"
     ],
-    "cwd": "[SLAVE_BUILD]",
-    "name": "read [SLAVE_BUILD]/copytree_example_tmp2/dummy_file"
+    "name": "read [TMP]/copytree_example_tmp2/dummy_file"
   },
   {
     "cmd": [
       "python",
       "-u",
       "\nimport glob\nimport sys\nwith open(sys.argv[1], 'w') as f:\n  f.write('\\n'.join(glob.glob(sys.argv[2])))\n",
       "/path/to/tmp/",
-      "[SLAVE_BUILD]/copytree_example_tmp/*"
+      "[TMP]/copytree_example_tmp/*"
     ],
-    "cwd": "[SLAVE_BUILD]",
     "name": "glob"
   },
   {
     "cmd": [
       "python",
       "-u",
       "\nimport shutil, sys\nshutil.rmtree(sys.argv[1])\n",
-      "[SLAVE_BUILD]/copytree_example_tmp"
+      "[TMP]/copytree_example_tmp"
     ],
-    "cwd": "[SLAVE_BUILD]",
     "name": "cleanup",
     "~followup_annotations": [
       "@@@STEP_LOG_LINE@python.inline@@@@",
       "@@@STEP_LOG_LINE@python.inline@import shutil, sys@@@",
       "@@@STEP_LOG_LINE@python.inline@shutil.rmtree(sys.argv[1])@@@",
       "@@@STEP_LOG_END@python.inline@@@"
     ]
   },
   {
     "cmd": [
       "python",
       "-u",
       "\nimport shutil, sys\nshutil.rmtree(sys.argv[1])\n",
-      "[SLAVE_BUILD]/copytree_example_tmp2"
+      "[TMP]/copytree_example_tmp2"
     ],
-    "cwd": "[SLAVE_BUILD]",
     "name": "cleanup2",
     "~followup_annotations": [
       "@@@STEP_LOG_LINE@python.inline@@@@",
       "@@@STEP_LOG_LINE@python.inline@import shutil, sys@@@",
       "@@@STEP_LOG_LINE@python.inline@shutil.rmtree(sys.argv[1])@@@",
       "@@@STEP_LOG_END@python.inline@@@"
     ]
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]