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

scripts/slave/recipes/gpu/build_and_test.expected/mac_debug.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "[BUILD]/scripts/slave/cleanup_temp.py"
     ],
     "name": "cleanup temp"
   },
   {
@@ skipping 67 matching lines @@
     ],
     "env": {
       "GYP_DEFINES": "archive_gpu_tests=1 blink_logging_always_on=1 clang=1 component=shared_library dcheck_always_on=1 disable_glibcxx_debug=1 ffmpeg_branding=Chrome gomadir='[BUILD]/goma' internal_gles2_conform_tests=1 proprietary_codecs=1 target_arch=x64 test_isolation_mode=prepare use_goma=1"
     },
     "name": "gclient runhooks"
   },
   {
     "cmd": [
       "python",
       "-u",
-      "[BUILD]/scripts/slave/recipe_modules/isolate/resources/find_isolated_tests.py",
+      "RECIPE_MODULE[isolate]/resources/find_isolated_tests.py",
       "--build-dir",
       "[SLAVE_BUILD]/src/out/Debug",
       "--clean-isolated-files"
     ],
     "name": "clean isolated files"
   },
   {
     "cmd": [
       "python",
       "-u",
@@ skipping 621 matching lines @@
       "json",
       "--output-dir",
       "/path/to/tmp/"
     ],
     "name": "gpu_rasterization_tests",
     "~followup_annotations": [
       "@@@STEP_TEXT@<br/>failures:<br/>Test.Test1<br/>@@@"
     ]
   }
 ]