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

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

 [
   {
     "cmd": [
       "python",
       "-u",
       "[BUILD]/scripts/slave/cleanup_temp.py"
     ],
     "name": "cleanup temp"
   },
   {
     "cmd": [
       "python",
       "-u",
       "[DEPOT_TOOLS]/gclient.py",
       "runhooks"
     ],
     "env": {
       "GYP_DEFINES": "archive_gpu_tests=1 blink_logging_always_on=1 clang=1 component=static_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/Release",
       "--clean-isolated-files"
     ],
     "name": "clean isolated files"
   },
   {
     "cmd": [
       "python",
       "-u",
@@ skipping 654 matching lines @@
       "[SLAVE_BUILD]/src/tools/swarming_client/run_isolated.py",
       "-H",
       "[dummy hash for tab_capture_end2end_tests]",
       "-I",
       "https://isolateserver.appspot.com",
       "--"
     ],
     "name": "tab_capture_end2end_tests"
   }
 ]