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

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

 [
   {
     "cmd": [
       "python",
       "-u",
       "[BUILD]/scripts/slave/bot_update.py",
       "--master",
       "chromium.webrtc",
       "--builder",
       "Linux Builder",
@@ 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 44 matching lines @@
       "--build_revision",
       "f27fede2220bcd326aee3e86ddfd4ebd0fe58cb9",
       "--factory-properties",
       "{\"blamelist\": [\"cool_dev1337@chromium.org\", \"hax@chromium.org\"], \"buildername\": \"Linux Builder\", \"buildnumber\": 571, \"mastername\": \"chromium.webrtc\", \"parent_buildername\": null, \"recipe\": \"webrtc/chromium\", \"revision\": \"321321\", \"slavename\": \"TestSlavename\", \"workdir\": \"/path/to/workdir/TestSlavename\"}",
       "--build-properties",
       "{\"blamelist\": [\"cool_dev1337@chromium.org\", \"hax@chromium.org\"], \"buildername\": \"Linux Builder\", \"buildnumber\": 571, \"mastername\": \"chromium.webrtc\", \"parent_buildername\": null, \"recipe\": \"webrtc/chromium\", \"revision\": \"321321\", \"slavename\": \"TestSlavename\", \"workdir\": \"/path/to/workdir/TestSlavename\"}"
     ],
     "name": "package build"
   }
 ]