Recipes: make cwd default to slave_build

scripts/slave/recipes/v8/auto_roll_push.expected/standard.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "[BUILD]/scripts/slave/cleanup_temp.py"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "name": "cleanup_temp"
   },
   {
     "cmd": [
       "python",
       "-u",
       "[BUILD]/scripts/slave/bot_update.py",
       "--master",
       "client.v8",
       "--builder",
       "TestBuilder",
       "--slave",
       "TestSlavename",
       "--spec",
       "cache_dir = None\nsolutions = [{'custom_vars': {'chromium_trunk': 'svn://svn-mirror.golo.chromium.org/chrome/trunk'}, 'deps_file': 'DEPS', 'managed': True, 'name': 'v8', 'url': 'https://chromium.googlesource.com/v8/v8'}]",
       "--root",
       "v8",
       "--revision_mapping_file",
       "{\"v8\": \"got_revision\"}",
       "--output_json",
       "/path/to/tmp/json",
       "--revision",
       "v8@HEAD",
       "--force",
       "--no_shallow"
     ],
+    "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\": \"v8\", @@@",
       "@@@STEP_LOG_LINE@json.output@  \"properties\": {@@@",
       "@@@STEP_LOG_LINE@json.output@    \"got_revision\": \"f2cbea7e89a45f46819777bb78a1f5bd0241f64c\", @@@",
       "@@@STEP_LOG_LINE@json.output@    \"got_revision_cp\": \"refs/heads/master@{#50110}\"@@@",
       "@@@STEP_LOG_LINE@json.output@  }, @@@",
       "@@@STEP_LOG_LINE@json.output@  \"root\": \"v8\", @@@",
       "@@@STEP_LOG_LINE@json.output@  \"step_text\": \"Some step text\"@@@",
       "@@@STEP_LOG_LINE@json.output@}@@@",
       "@@@STEP_LOG_END@json.output@@@",
       "@@@SET_BUILD_PROPERTY@got_revision@\"f2cbea7e89a45f46819777bb78a1f5bd0241f64c\"@@@",
       "@@@SET_BUILD_PROPERTY@got_revision_cp@\"refs/heads/master@{#50110}\"@@@"
     ]
   },
   {
     "cmd": [
       "python",
       "-u",
       "[BUILD]/scripts/tools/runit.py",
       "[BUILD]/scripts/tools/pycurl.py",
       "https://v8-roll.appspot.com/status"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "name": "check roll status",
     "stdout": "/path/to/tmp/",
     "~followup_annotations": [
       "@@@STEP_TEXT@Pushing activated@@@",
       "@@@STEP_LOG_LINE@stdout@1@@@",
       "@@@STEP_LOG_END@stdout@@@"
     ]
   },
   {
     "cmd": [
       "python",
       "-u",
       "[SLAVE_BUILD]/v8/tools/release/auto_push.py",
       "--author",
       "v8-autoroll@chromium.org",
       "--reviewer",
       "v8-autoroll@chromium.org",
       "--push",
       "--work-dir",
       "[SLAVE_BUILD]/workdir"
     ],
     "cwd": "[SLAVE_BUILD]/v8",
     "name": "push candidate"
   }
 ]