Recipes: make cwd default to slave_build

scripts/slave/recipes/webrtc/standalone.expected/client_webrtc_ios64_debug.json

Index: scripts/slave/recipes/webrtc/standalone.expected/client_webrtc_ios64_debug.json
diff --git a/scripts/slave/recipes/webrtc/standalone.expected/client_webrtc_ios64_debug.json b/scripts/slave/recipes/webrtc/standalone.expected/client_webrtc_ios64_debug.json
index bda915aa6dd68e6eb7560e77e0491120abacf467..1e5df90a5c62b0534653f3c3c6665970ee56b708 100644
--- a/scripts/slave/recipes/webrtc/standalone.expected/client_webrtc_ios64_debug.json
+++ b/scripts/slave/recipes/webrtc/standalone.expected/client_webrtc_ios64_debug.json
@@ -21,6 +21,7 @@
       "--revision",
       "src@12345"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "name": "bot_update",
     "~followup_annotations": [
       "@@@STEP_TEXT@Some step text@@@",
@@ -47,6 +48,7 @@
       "RECIPE_MODULE[webrtc]/resources/cleanup_files.py",
       "[SLAVE_BUILD]/src/out"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "name": "clean test output files"
   },
   {
@@ -55,6 +57,7 @@
       "-u",
       "[BUILD]/scripts/slave/cleanup_temp.py"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "name": "cleanup_temp"
   },
   {
@@ -64,6 +67,7 @@
       "[DEPOT_TOOLS]/gclient.py",
       "runhooks"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "env": {
       "GYP_CROSSCOMPILE": "1",
       "GYP_DEFINES": "OS=ios build_with_libjingle=1 chromium_ios_signing=0 clang=1 component=static_library dcheck_always_on=1 gomadir='[BUILD]/goma' key_id='' mac_sdk=10.9 target_arch=arm64 use_goma=1",
@@ -89,6 +93,7 @@
       "--",
       "All"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "name": "compile"
   }
 ]