Recipes: make cwd default to slave_build

scripts/slave/recipes/infra/publish_tarball.expected/basic.json

Index: scripts/slave/recipes/infra/publish_tarball.expected/basic.json
diff --git a/scripts/slave/recipes/infra/publish_tarball.expected/basic.json b/scripts/slave/recipes/infra/publish_tarball.expected/basic.json
index d885304fd04e29f2ae4a2c01648aab506a19df89..9e4a6b2c318e5011f831e17d8f0b77e2d53bf374 100644
--- a/scripts/slave/recipes/infra/publish_tarball.expected/basic.json
+++ b/scripts/slave/recipes/infra/publish_tarball.expected/basic.json
@@ -23,6 +23,7 @@
       "--force",
       "--with_branch_heads"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "name": "bot_update",
     "~followup_annotations": [
       "@@@STEP_TEXT@Some step text@@@",
@@ -91,6 +92,7 @@
       "[TMP_BASE]/export_tarball_tmp_1/chromium-38.0.2125.122.tar.xz",
       "gs://chromium-browser-official/chromium-38.0.2125.122.tar.xz"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "name": "gsutil upload",
     "~followup_annotations": [
       "@@@STEP_LINK@gsutil.upload@https://storage.cloud.google.com/chromium-browser-official/chromium-38.0.2125.122.tar.xz@@@"
@@ -103,6 +105,7 @@
       "\nimport os, sys\nfrom common import chromium_utils\n\nif os.path.exists(sys.argv[1]):\n  chromium_utils.RemoveDirectory(sys.argv[1])\n",
       "[TMP_BASE]/export_tarball_tmp_1"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "name": "rmtree temp dir",
     "~followup_annotations": [
       "@@@STEP_LOG_LINE@python.inline@@@@",