Recipes: make cwd default to slave_build

scripts/slave/recipes/boringssl.expected/win32.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "[BUILD]\\scripts\\slave\\bot_update.py",
       "--master",
       "client.boringssl",
       "--builder",
       "win32",
       "--slave",
       "slavename",
       "--spec",
       "cache_dir = None\nsolutions = [{'deps_file': 'util/bot/DEPS', 'managed': True, 'name': 'boringssl', 'url': 'https://boringssl.googlesource.com/boringssl.git'}]",
       "--root",
       "boringssl",
       "--revision_mapping_file",
       "{}",
       "--output_json",
       "/path/to/tmp/json",
       "--revision",
       "boringssl@HEAD",
       "--force"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "name": "bot_update",
     "~followup_annotations": [
       "@@@STEP_TEXT@Some step text@@@",
       "@@@STEP_LOG_LINE@json.output@{@@@",
       "@@@STEP_LOG_LINE@json.output@  \"did_run\": true, @@@",
       "@@@STEP_LOG_LINE@json.output@  \"patch_failure\": false, @@@",
       "@@@STEP_LOG_LINE@json.output@  \"patch_root\": \"boringssl\", @@@",
       "@@@STEP_LOG_LINE@json.output@  \"properties\": {}, @@@",
       "@@@STEP_LOG_LINE@json.output@  \"root\": \"boringssl\", @@@",
       "@@@STEP_LOG_LINE@json.output@  \"step_text\": \"Some step text\"@@@",
       "@@@STEP_LOG_LINE@json.output@}@@@",
       "@@@STEP_LOG_END@json.output@@@"
     ]
   },
   {
     "cmd": [
       "python",
       "-u",
       "[DEPOT_TOOLS]\\gclient.py",
       "runhooks"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "name": "gclient runhooks"
   },
   {
     "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]\\boringssl\\build",
       "511"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "name": "makedirs mkdir",
     "~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)@@@",
@@ skipping 23 matching lines @@
       "python",
       "-u",
       "[SLAVE_BUILD]\\boringssl\\util\\bot\\go\\env.py",
       "python",
       "[SLAVE_BUILD]\\boringssl\\util\\bot\\vs_env.py",
       "x86",
       "ninja",
       "-C",
       "[SLAVE_BUILD]\\boringssl\\build"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "name": "ninja"
   },
   {
     "cmd": [
       "python",
       "-u",
       "[SLAVE_BUILD]\\boringssl\\util\\bot\\go\\env.py",
       "python",
       "[SLAVE_BUILD]\\boringssl\\util\\bot\\vs_env.py",
       "x86",
@@ skipping 110 matching lines @@
       "@@@STEP_LOG_LINE@test_utils.test_results@        \"actual\": \"PASS\", @@@",
       "@@@STEP_LOG_LINE@test_utils.test_results@        \"expected\": \"PASS\"@@@",
       "@@@STEP_LOG_LINE@test_utils.test_results@      }@@@",
       "@@@STEP_LOG_LINE@test_utils.test_results@    }@@@",
       "@@@STEP_LOG_LINE@test_utils.test_results@  }@@@",
       "@@@STEP_LOG_LINE@test_utils.test_results@}@@@",
       "@@@STEP_LOG_END@test_utils.test_results@@@"
     ]
   }
 ]