Recipes: make cwd default to slave_build

scripts/slave/recipes/v8.expected/full_client_v8_NaCl_V8_Linux64___canary.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "[BUILD]/scripts/slave/bot_update.py",
       "--master",
       "client.v8",
       "--builder",
       "NaCl V8 Linux64 - canary",
       "--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@20123",
       "--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": "target_arch=x64 v8_enable_i18n_support=0 v8_target_arch=nacl_x64"
     },
     "name": "gclient runhooks"
   },
   {
     "cmd": [
       "python",
       "-u",
       "[BUILD]/scripts/slave/cleanup_temp.py"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "name": "cleanup_temp"
   },
   {
     "cmd": [
       "python",
       "-u",
       "[BUILD]/scripts/slave/update_nacl_sdk.py",
       "--pepper-channel",
       "canary"
     ],
     "cwd": "[SLAVE_BUILD]",
     "name": "update NaCl SDK"
   },
   {
     "cmd": [
       "python",
       "-u",
       "[BUILD]/scripts/slave/compile.py",
       "--target",
       "Release",
       "--src-dir",
       "[SLAVE_BUILD]/v8",
       "--build-tool",
       "make",
       "--",
       "-C",
       "..",
       "nacl_x64.release"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "env": {
       "NACL_SDK_ROOT": "[SLAVE_BUILD]/nacl_sdk/pepper_current"
     },
     "name": "compile"
   },
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_MODULE[v8]/resources/v8testing.py",
@@ skipping 117 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@@@"
     ]
   }
 ]