[loader] Make recipe engine support examples/ module subdir

recipe_modules/properties/examples/full.expected/buildbot_tryserver.json

 [
   {
     "cmd": [
       "echo",
       "None",
       "'thing'"
     ],
     "name": "echo"
   },
   {
     "cmd": [
       "echo",
       "('blamelist', ['cool_dev1337@chromium.org', 'hax@chromium.org'])",
       "('bot_id', 'test_bot')",
       "('branch', '')",
       "('buildbotURL', 'http://c.org/p/cr/')",
       "('buildername', 'TestBuilder')",
       "('buildnumber', 571)",
       "('foo.bar-bam', 'thing')",
       "('issue', 12853011)",
       "('mastername', 'chromium.testing.master')",
       "('patch_project', 'chromium')",
       "('patchset', 1)",
       "('project', 'chrome')",
-      "('recipe', 'properties:example')",
+      "('recipe', 'properties:examples/full')",
       "('repository', '')",
       "('requester', 'commit-bot@chromium.org')",
       "('revision', 'HEAD')",
       "('rietveld', 'https://codereview.chromium.org')",
       "('slavename', 'TestSlavename')",
       "('test_prop', None)",
       "('workdir', '/path/to/workdir/TestSlavename')"
     ],
     "name": "echo all"
   },
@@ skipping 28 matching lines @@
   {
     "cmd": [
       "echo",
       "None"
     ],
     "name": "echo test_prop"
   },
   {
     "cmd": [
       "echo",
-      "'properties:example'"
+      "'properties:examples/full'"
     ],
     "name": "echo recipe"
   },
   {
     "cmd": [
       "echo",
       "'chromium.testing.master'"
     ],
     "name": "echo mastername"
   },
@@ skipping 87 matching lines @@
       "'test_bot'"
     ],
     "name": "echo bot_id"
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]