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

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

 [
   {
     "cmd": [
       "python",
       "-u",
       "[BUILD]/scripts/slave/bot_update.py",
       "--master",
       "chromium.perf",
       "--builder",
       "Android One Perf",
@@ skipping 205 matching lines @@
     ],
     "env": {
       "PATH": "[SLAVE_BUILD]/src/third_party/android_tools/sdk/platform-tools:[SLAVE_BUILD]/src/build/android:%(PATH)s"
     },
     "name": "provision_devices"
   },
   {
     "cmd": [
       "python",
       "-u",
-      "[BUILD]/scripts/slave/recipe_modules/adb/resources/list_devices.py",
+      "RECIPE_MODULE[adb]/resources/list_devices.py",
       "['[SLAVE_BUILD]/src/third_party/android_tools/sdk/platform-tools/adb', 'devices']",
       "/path/to/tmp/json"
     ],
     "name": "List adb devices",
     "~followup_annotations": [
       "@@@STEP_LOG_LINE@json.output@[@@@",
       "@@@STEP_LOG_LINE@json.output@  \"014E1F310401C009\", @@@",
       "@@@STEP_LOG_LINE@json.output@  \"014E1F310401C010\"@@@",
       "@@@STEP_LOG_LINE@json.output@]@@@",
       "@@@STEP_LOG_END@json.output@@@"
@@ skipping 209 matching lines @@
       "@@@STEP_LOG_LINE@python.inline@import glob, os, sys@@@",
       "@@@STEP_LOG_LINE@python.inline@for report in glob.glob(sys.argv[1]):@@@",
       "@@@STEP_LOG_LINE@python.inline@  with open(report, 'r') as f:@@@",
       "@@@STEP_LOG_LINE@python.inline@    for l in f.readlines():@@@",
       "@@@STEP_LOG_LINE@python.inline@      print l@@@",
       "@@@STEP_LOG_LINE@python.inline@  os.remove(report)@@@",
       "@@@STEP_LOG_END@python.inline@@@"
     ]
   }
 ]