Recipes: make cwd default to slave_build

scripts/slave/recipe_modules/bisect_tester/example.expected/basic.json

 [
   {
     "cmd": [
       "dummy_command.py"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "name": "Fake failing test.",
     "~followup_annotations": [
       "step returned non-zero exit code: 4",
       "@@@STEP_FAILURE@@@"
     ]
   },
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_MODULE[bisect_tester]/resources/put_temp.py"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "name": "saving json to temp file",
     "stdin": "{\"output\": \"\", \"results\": \"Test failed with error code: 4\"}",
     "stdout": "/path/to/tmp/"
   },
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_MODULE[gsutil]/resources/gsutil_wrapper.py",
       "--",
       "[DEPOT_TOOLS]/gsutil.py",
       "--force-version",
       "3.25",
       "--",
       "cp",
       "dummy_location.json",
       "gs://chrome-perf/bisect-results/dummy.results"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "name": "gsutil upload",
     "~followup_annotations": [
       "@@@STEP_LINK@gsutil.upload@https://storage.cloud.google.com/chrome-perf/bisect-results/dummy.results@@@"
     ]
   },
   {
     "name": "$final_result",
     "reason": "Test Failed",
     "status_code": 1
   }
 ]