Recipes: make cwd default to slave_build

scripts/slave/recipes/v8.expected/full_tryserver_v8_v8_win_rel.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "[BUILD]\\scripts\\slave\\kill_processes.py"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "name": "taskkill"
   },
   {
     "cmd": [
       "python",
       "-u",
       "[BUILD]\\scripts\\slave\\bot_update.py",
       "--master",
       "tryserver.v8",
       "--builder",
       "v8_win_rel",
       "--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\"}",
       "--patch_url",
       "svn://svn-mirror.golo.chromium.org/patch",
       "--output_json",
       "/path/to/tmp/json",
       "--revision",
       "v8@12345",
       "--no_shallow",
       "--output_manifest"
     ],
+    "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@  \"manifest\": {@@@",
       "@@@STEP_LOG_LINE@json.output@    \"v8\": {@@@",
       "@@@STEP_LOG_LINE@json.output@      \"repository\": \"https://fake.org/v8.git\", @@@",
       "@@@STEP_LOG_LINE@json.output@      \"revision\": \"f2cbea7e89a45f46819777bb78a1f5bd0241f64c\"@@@",
       "@@@STEP_LOG_LINE@json.output@    }@@@",
@@ skipping 12 matching lines @@
       "@@@SET_BUILD_PROPERTY@got_revision_cp@\"refs/heads/master@{#50110}\"@@@"
     ]
   },
   {
     "cmd": [
       "python",
       "-u",
       "[DEPOT_TOOLS]\\gclient.py",
       "runhooks"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "env": {
       "GYP_DEFINES": "dcheck_always_on=1 fastbuild=1 target_arch=ia32 v8_target_arch=ia32",
       "GYP_MSVS_VERSION": "2013"
     },
     "name": "gclient runhooks"
   },
   {
     "cmd": [
       "python",
       "-u",
       "[BUILD]\\scripts\\slave\\cleanup_temp.py"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "name": "cleanup_temp"
   },
   {
     "cmd": [
       "python",
       "-u",
       "[BUILD]\\scripts\\slave\\compile.py",
       "--target",
       "Release",
       "--src-dir",
       "[SLAVE_BUILD]\\v8",
       "--build-tool",
       "vs",
       "--"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "name": "compile"
   },
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_MODULE[v8]\\resources\\v8testing.py",
       "--target",
       "Release",
       "--arch",
@@ skipping 95 matching lines @@
       "@@@STEP_LOG_LINE@durations@Command: d8 -f mjsunit/Cool.Test@@@",
       "@@@STEP_LOG_LINE@durations@Duration: 01:01:002@@@",
       "@@@STEP_LOG_LINE@durations@Test: mjsunit/Cool.Test2@@@",
       "@@@STEP_LOG_LINE@durations@Flags: -f -g@@@",
       "@@@STEP_LOG_LINE@durations@Command: d8 -f mjsunit/Cool.Test2@@@",
       "@@@STEP_LOG_LINE@durations@Duration: 00:00:101@@@",
       "@@@STEP_LOG_END@durations@@@"
     ]
   }
 ]