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

scripts/slave/recipes/chromium.expected/full_chromium_webkit_WebKit_XP.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "[BUILD]\\scripts\\slave\\kill_processes.py"
     ],
     "name": "taskkill"
   },
   {
@@ skipping 170 matching lines @@
       "{\"blamelist\": [\"cool_dev1337@chromium.org\", \"hax@chromium.org\"], \"buildername\": \"WebKit XP\", \"buildnumber\": 571, \"mastername\": \"chromium.webkit\", \"parent_build_archive_url\": \"gs://test-domain/test-archive.zip\", \"parent_buildername\": \"WebKit Win Builder\", \"parent_got_revision\": \"1111111\", \"recipe\": \"chromium\", \"slavename\": \"TestSlavename\", \"swarm_hashes\": {\"browser_tests\": \"ffffffffffffffffffffffffffffffffffffffff\"}, \"workdir\": \"/path/to/workdir/TestSlavename\"}",
       "--build-properties",
       "{\"blamelist\": [\"cool_dev1337@chromium.org\", \"hax@chromium.org\"], \"buildername\": \"WebKit XP\", \"buildnumber\": 571, \"mastername\": \"chromium.webkit\", \"parent_build_archive_url\": \"gs://test-domain/test-archive.zip\", \"parent_buildername\": \"WebKit Win Builder\", \"parent_got_revision\": \"1111111\", \"recipe\": \"chromium\", \"slavename\": \"TestSlavename\", \"swarm_hashes\": {\"browser_tests\": \"ffffffffffffffffffffffffffffffffffffffff\"}, \"workdir\": \"/path/to/workdir/TestSlavename\"}"
     ],
     "name": "extract build"
   },
   {
     "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",
       "--output-json",
       "/path/to/tmp/json"
     ],
     "name": "find isolated tests",
     "~followup_annotations": [
       "@@@STEP_LOG_LINE@json.output@{@@@",
       "@@@STEP_LOG_LINE@json.output@  \"dummy_target_1\": \"[dummy hash for dummy_target_1]\", @@@",
       "@@@STEP_LOG_LINE@json.output@  \"dummy_target_2\": \"[dummy hash for dummy_target_2]\"@@@",
@@ skipping 147 matching lines @@
     "~followup_annotations": [
       "@@@STEP_LINK@layout_test_results@https://storage.googleapis.com/chromium-layout-test-archives/WebKit_XP/571/layout-test-results/results.html@@@",
       "@@@STEP_LINK@(zip)@https://storage.googleapis.com/chromium-layout-test-archives/WebKit_XP/571/layout-test-results.zip@@@"
     ]
   },
   {
     "allow_subannotations": true,
     "cmd": [
       "python",
       "-u",
-      "[BUILD]\\scripts\\slave\\recipe_modules\\swarming\\resources\\collect_gtest_task.py",
+      "RECIPE_MODULE[swarming]\\resources\\collect_gtest_task.py",
       "--swarming-client-dir",
       "[SLAVE_BUILD]\\src\\tools\\swarming_client",
       "--temp-root-dir",
       "[TMP_BASE]",
       "--merged-test-output",
       "/path/to/tmp/json",
       "--",
       "collect",
       "--swarming",
       "https://chromium-swarm.appspot.com",
       "--decorate",
       "--print-status-updates",
       "--shards",
       "1",
       "browser_tests/Windows-7-SP1/ffffffffff/WebKit XP/571"
     ],
     "name": "browser_tests"
   },
   {
     "cmd": [
       "python",
       "-u",
       "[BUILD]\\scripts\\slave\\process_dumps.py",
       "--target",
       "Release"
     ],
     "name": "process_dumps"
   }
 ]