Recipes: make cwd default to slave_build

scripts/slave/recipes/webrtc/chromium.expected/chromium_webrtc_Mac_Builder.json

Index: scripts/slave/recipes/webrtc/chromium.expected/chromium_webrtc_Mac_Builder.json
diff --git a/scripts/slave/recipes/webrtc/chromium.expected/chromium_webrtc_Mac_Builder.json b/scripts/slave/recipes/webrtc/chromium.expected/chromium_webrtc_Mac_Builder.json
index ddf0fdd7811242b52b3fbc172b5c92481d5c5b29..39b71eb20c267ffe69beef43008b50ae1b109e26 100644
--- a/scripts/slave/recipes/webrtc/chromium.expected/chromium_webrtc_Mac_Builder.json
+++ b/scripts/slave/recipes/webrtc/chromium.expected/chromium_webrtc_Mac_Builder.json
@@ -21,6 +21,7 @@
       "--revision",
       "src@c321321"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "name": "bot_update",
     "~followup_annotations": [
       "@@@STEP_TEXT@Some step text@@@",
@@ -75,6 +76,7 @@
       "RECIPE_MODULE[webrtc]/resources/cleanup_files.py",
       "[SLAVE_BUILD]/src/out"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "name": "clean test output files"
   },
   {
@@ -83,6 +85,7 @@
       "-u",
       "[BUILD]/scripts/slave/cleanup_temp.py"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "name": "cleanup_temp"
   },
   {
@@ -92,6 +95,7 @@
       "[DEPOT_TOOLS]/gclient.py",
       "runhooks"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "env": {
       "GYP_DEFINES": "blink_logging_always_on=1 clang=1 component=static_library dcheck_always_on=1 gomadir='[BUILD]/goma' target_arch=x64 use_goma=1"
     },
@@ -115,6 +119,7 @@
       "--",
       "chromium_builder_webrtc"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "name": "compile"
   },
   {
@@ -134,10 +139,12 @@
       "--build-properties",
       "{\"blamelist\": [\"cool_dev1337@chromium.org\", \"hax@chromium.org\"], \"buildername\": \"Mac Builder\", \"buildnumber\": 571, \"mastername\": \"chromium.webrtc\", \"parent_buildername\": null, \"recipe\": \"webrtc/chromium\", \"revision\": \"c321321\", \"slavename\": \"TestSlavename\", \"workdir\": \"/path/to/workdir/TestSlavename\"}"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "name": "package build"
   },
   {
     "cmd": [],
+    "cwd": "[SLAVE_BUILD]",
     "name": "trigger",
     "trigger_specs": [
       {