Changed recipe_modules base paths to be abstract entities in their own right.

scripts/slave/recipes/cronet.expected/android_cronet_arm64_builder.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "\nimport os, sys\n\nbuild_path = sys.argv[1]\nif os.path.exists(build_path):\n  for (path, dir, files) in os.walk(build_path):\n    for cur_file in files:\n      if cur_file.endswith('index.lock'):\n        path_to_file = os.path.join(path, cur_file)\n        print 'deleting %s' % path_to_file\n        os.remove(path_to_file)\n",
       "[SLAVE_BUILD]"
     ],
     "name": "cleanup index.lock",
     "~followup_annotations": [
@@ skipping 165 matching lines @@
     ],
     "env": {
       "PATH": "[SLAVE_BUILD]/src/third_party/android_tools/sdk/platform-tools:[SLAVE_BUILD]/src/build/android:%(PATH)s"
     },
     "name": "compile"
   },
   {
     "cmd": [
       "python",
       "-u",
-      "[BUILD]/scripts/slave/recipe_modules/gsutil/resources/gsutil_wrapper.py",
+      "RECIPE_MODULE[gsutil]/resources/gsutil_wrapper.py",
       "--",
       "[DEPOT_TOOLS]/gsutil.py",
       "--force-version",
       "3.25",
       "--",
       "cp",
       "[SLAVE_BUILD]/src/out/Release/cronet/VERSION",
       "gs://chromium-cronet/android/cronet-Release-4f4b02f6b7fa20a3a25682c457bbc8ad589c8a00/VERSION"
     ],
     "name": "gsutil upload_cronet_version",
     "~followup_annotations": [
       "@@@STEP_LINK@Cronet version@https://storage.cloud.google.com/chromium-cronet/android/cronet-Release-4f4b02f6b7fa20a3a25682c457bbc8ad589c8a00/VERSION@@@"
     ]
   },
   {
     "cmd": [
       "python",
       "-u",
-      "[BUILD]/scripts/slave/recipe_modules/gsutil/resources/gsutil_wrapper.py",
+      "RECIPE_MODULE[gsutil]/resources/gsutil_wrapper.py",
       "--",
       "[DEPOT_TOOLS]/gsutil.py",
       "--force-version",
       "3.25",
       "--",
       "cp",
       "-R",
       "[SLAVE_BUILD]/src/out/Release/cronet",
       "gs://chromium-cronet/android/cronet-Release-4f4b02f6b7fa20a3a25682c457bbc8ad589c8a00"
     ],
     "name": "gsutil upload_cronet_package",
     "~followup_annotations": [
       "@@@STEP_LINK@Cronet package@https://storage.cloud.google.com/chromium-cronet/android/cronet-Release-4f4b02f6b7fa20a3a25682c457bbc8ad589c8a00@@@"
     ]
   }
 ]