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

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

 [
   {
     "cmd": [
       "python",
       "-u",
       "[BUILD]\\scripts\\slave\\kill_processes.py"
     ],
     "name": "taskkill"
   },
   {
@@ skipping 63 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 197 matching lines @@
     "cmd": [
       "python",
       "-u",
       "[BUILD]\\scripts\\slave\\process_dumps.py",
       "--target",
       "Release"
     ],
     "name": "process_dumps"
   }
 ]