depot_tools: add infra_paths recipe module for infra-specific paths

recipe_modules/git/example.expected/count-objects_with_bad_output_fails_build.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_MODULE[depot_tools::git]/resources/git_setup.py",
       "--path",
-      "[SLAVE_BUILD]/src",
+      "[CWD]/src",
       "--url",
       "https://chromium.googlesource.com/chromium/src.git"
     ],
-    "cwd": "[SLAVE_BUILD]",
     "name": "git setup"
   },
   {
     "cmd": [
       "git",
       "retry",
       "fetch",
       "origin",
       "master",
       "--recurse-submodules"
     ],
-    "cwd": "[SLAVE_BUILD]/src",
+    "cwd": "[CWD]/src",
     "name": "git fetch"
   },
   {
     "cmd": [
       "git",
       "checkout",
       "-f",
       "FETCH_HEAD"
     ],
-    "cwd": "[SLAVE_BUILD]/src",
+    "cwd": "[CWD]/src",
     "name": "git checkout"
   },
   {
     "cmd": [
       "git",
       "rev-parse",
       "HEAD"
     ],
-    "cwd": "[SLAVE_BUILD]/src",
+    "cwd": "[CWD]/src",
     "name": "read revision",
     "stdout": "/path/to/tmp/",
     "~followup_annotations": [
       "@@@STEP_TEXT@<br/>checked out 'deadbeef'<br/>@@@"
     ]
   },
   {
     "cmd": [
       "git",
       "clean",
       "-f",
       "-d",
       "-x"
     ],
-    "cwd": "[SLAVE_BUILD]/src",
+    "cwd": "[CWD]/src",
     "name": "git clean"
   },
   {
     "cmd": [
       "git",
       "submodule",
       "sync"
     ],
-    "cwd": "[SLAVE_BUILD]/src",
+    "cwd": "[CWD]/src",
     "name": "submodule sync"
   },
   {
     "cmd": [
       "git",
       "submodule",
       "update",
       "--init",
       "--recursive"
     ],
-    "cwd": "[SLAVE_BUILD]/src",
+    "cwd": "[CWD]/src",
     "name": "submodule update"
   },
   {
     "cmd": [
       "git",
       "-c",
       "foo=bar",
       "count-objects",
       "-v"
     ],
-    "cwd": "[SLAVE_BUILD]/src",
+    "cwd": "[CWD]/src",
     "name": "count-objects",
     "stdout": "/path/to/tmp/",
     "~followup_annotations": [
       "@@@STEP_LOG_LINE@exception@ValueError(\"invalid literal for long() with base 10: 'xxx'\",)@@@",
       "@@@STEP_LOG_END@exception@@@",
       "@@@STEP_WARNINGS@@@"
     ]
   },
   {
     "name": "$result",
     "reason": "count-objects failed: invalid literal for long() with base 10: 'xxx'",
     "status_code": 1
   }
 ]