Recipes: make cwd default to slave_build

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

Index: scripts/slave/recipes/webrtc/standalone.expected/client_webrtc_fyi_android_builder__dbg_.json
diff --git a/scripts/slave/recipes/webrtc/standalone.expected/client_webrtc_fyi_android_builder__dbg_.json b/scripts/slave/recipes/webrtc/standalone.expected/client_webrtc_fyi_android_builder__dbg_.json
index 29314432a80ca50fe1f2c7a52a79ee47c6f1b938..5c806a79c96356f5dbb81c54e69fefb4328542f9 100644
--- a/scripts/slave/recipes/webrtc/standalone.expected/client_webrtc_fyi_android_builder__dbg_.json
+++ b/scripts/slave/recipes/webrtc/standalone.expected/client_webrtc_fyi_android_builder__dbg_.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"
   },
   {
@@ -59,6 +61,7 @@
       "[SLAVE_BUILD]/src/out/build_product.zip",
       "[SLAVE_BUILD]/src"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "name": "clean local files",
     "~followup_annotations": [
       "@@@STEP_LOG_LINE@python.inline@@@@",
@@ -83,6 +86,7 @@
       "[DEPOT_TOOLS]/gclient.py",
       "runhooks"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "env": {
       "GYP_CROSSCOMPILE": "1",
       "GYP_DEFINES": "OS=android component=static_library fastbuild=1 gomadir='[BUILD]/goma' target_arch=arm use_goma=1",
@@ -107,6 +111,7 @@
       "[BUILD]/goma",
       "--"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "env": {
       "PATH": "[SLAVE_BUILD]/src/third_party/android_tools/sdk/platform-tools:[SLAVE_BUILD]/src/build/android:%(PATH)s"
     },
@@ -129,10 +134,12 @@
       "--build-properties",
       "{\"BUILD_CONFIG\": \"Debug\", \"buildername\": \"Android Builder (dbg)\", \"buildnumber\": 1337, \"mastername\": \"client.webrtc.fyi\", \"recipe\": \"webrtc/standalone\", \"revision\": \"12345\", \"slavename\": \"slavename\"}"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "name": "package build"
   },
   {
     "cmd": [],
+    "cwd": "[SLAVE_BUILD]",
     "name": "trigger",
     "trigger_specs": [
       {