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

scripts/slave/recipes/webrtc/chromium.expected/chromium_webrtc_Linux_Tester_failing_test.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "[BUILD]/scripts/slave/bot_update.py",
       "--master",
       "chromium.webrtc",
       "--builder",
       "Linux Tester",
@@ skipping 55 matching lines @@
       "@@@SET_BUILD_PROPERTY@got_libvpx_revision_cp@\"refs/heads/master@{#11245}\"@@@",
       "@@@SET_BUILD_PROPERTY@got_revision_cp@\"refs/heads/master@{#170242}\"@@@",
       "@@@SET_BUILD_PROPERTY@got_webkit_revision_cp@\"refs/heads/master@{#124383}\"@@@",
       "@@@SET_BUILD_PROPERTY@got_libjingle_revision_cp@\"refs/heads/master@{#134440}\"@@@"
     ]
   },
   {
     "cmd": [
       "python",
       "-u",
-      "[BUILD]/scripts/slave/recipe_modules/webrtc/resources/cleanup_files.py",
+      "RECIPE_MODULE[webrtc]/resources/cleanup_files.py",
       "[SLAVE_BUILD]/src/out"
     ],
     "name": "clean test output files"
   },
   {
     "cmd": [
       "python",
       "-u",
       "[BUILD]/scripts/slave/cleanup_temp.py"
     ],
@@ skipping 205 matching lines @@
       "content_unittests"
     ],
     "name": "content_unittests"
   },
   {
     "name": "$final_result",
     "reason": "1 out of 3 aggregated steps failed. Failures: Step('browser_tests') failed with return_code 1",
     "status_code": 1
   }
 ]