depot_tools: add infra_paths recipe module for infra-specific paths

recipe_modules/tryserver/example.expected/with_wrong_patch.json

 [
   {
     "cmd": [
       "RECIPE_PACKAGE_REPO[depot_tools]\\bootstrap\\win\\win_tools.bat"
     ],
     "cwd": "RECIPE_PACKAGE_REPO[depot_tools]",
     "name": "ensure git tooling on windows"
   },
   {
     "cmd": [
       "RECIPE_PACKAGE_REPO[depot_tools]\\git.bat",
       "diff",
       "--cached",
       "--name-only"
     ],
-    "cwd": "[SLAVE_BUILD]",
+    "cwd": "[CWD]",
     "name": "git diff to analyze patch",
     "stdout": "/path/to/tmp/",
     "~followup_annotations": [
       "@@@STEP_LOG_LINE@files@foo.cc@@@",
       "@@@STEP_LOG_END@files@@@"
     ]
   },
   {
     "cmd": [
       "python",
       "-u",
       "import sys; sys.exit(1)"
     ],
-    "cwd": "[SLAVE_BUILD]",
     "name": "fail",
     "~followup_annotations": [
       "step returned non-zero exit code: 1",
       "@@@STEP_TEXT@foo@@@",
       "@@@STEP_FAILURE@@@",
       "@@@SET_BUILD_PROPERTY@failure_hash@\"c2311ad770732eade3d2f48247abd147e40a70e7\"@@@"
     ]
   },
   {
     "name": "$result",
     "reason": "Step('fail') failed with return_code 1",
     "status_code": 1
   }
 ]