Re-enable DepsCache using GOMA_DEPS_CACHE_FILE

scripts/slave/recipes/ios/unified_builder_tester.expected/goma.json

 [
   {
     "cmd": [
       "RECIPE_PACKAGE_REPO[build]/scripts/slave/ios/host_info.py",
       "--json-file",
       "/path/to/tmp/json"
     ],
     "name": "host and tools info",
     "~followup_annotations": [
       "@@@STEP_TEXT@<br />OS X 1.2.3, Xcode 6.7.8 (5D342509a)@@@",
@@ skipping 294 matching lines @@
       "--src-dir",
       "[BUILDER_CACHE]/ios/src",
       "--goma-cache-dir",
       "[GOMA_CACHE]",
       "--buildbot-buildername",
       "ios",
       "--buildbot-mastername",
       "chromium.fake",
       "--buildbot-slavename",
       "fake-vm",
-      "--goma-deps-cache-dir",
-      "[GOMA_DEPS_CACHE]",
+      "--goma-deps-cache-file",
+      "ios.gomadeps",
       "--compiler",
       "goma-clang",
       "--goma-jsonstatus",
       "/path/to/tmp/json",
       "--goma-service-account-json-file",
       "/creds/service_accounts/service-account-goma-client.json",
       "--goma-dir",
       "[CACHE]/cipd/goma",
       "--",
       "All"
     ],
     "cwd": "[BUILDER_CACHE]/ios/src/out/Release-iphoneos",
     "env": {
       "GOMA_SERVICE_ACCOUNT_JSON_FILE": "/creds/service_accounts/service-account-goma-client.json"
     },
     "name": "compile",
     "~followup_annotations": [
       "@@@STEP_LOG_LINE@json.output (invalid)@null@@@",
       "@@@STEP_LOG_END@json.output (invalid)@@@"
     ]
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]