[loader] Make recipe engine support examples/ module subdir

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

 [
   {
     "cmd": [
       "echo",
       "None",
       "'thing'"
     ],
     "name": "echo"
   },
   {
     "cmd": [
       "echo",
       "('blamelist', ['cool_dev1337@chromium.org', 'hax@chromium.org'])",
       "('bot_id', 'test_bot')",
       "('buildbotURL', 'http://c.org/p/cr/')",
       "('buildername', 'TestBuilder')",
       "('buildnumber', 571)",
       "('foo.bar-bam', 'thing')",
       "('mastername', 'chromium.testing.master')",
       "('patch_branch', 'master')",
       "('patch_gerrit_url', 'https://gerrit.my.host')",
       "('patch_issue', 989898)",
       "('patch_project', 'custom')",
       "('patch_ref', 'refs/changes/98/989898/3')",
       "('patch_repository_url', 'https://git.my.host/custom')",
       "('patch_set', 3)",
       "('patch_storage', 'gerrit')",
-      "('recipe', 'properties:example')",
+      "('recipe', 'properties:examples/full')",
       "('slavename', 'TestSlavename')",
       "('test_prop', None)",
       "('workdir', '/path/to/workdir/TestSlavename')"
     ],
     "name": "echo all"
   },
   {
     "cmd": [
       "echo",
       "3"
@@ skipping 45 matching lines @@
   {
     "cmd": [
       "echo",
       "'https://git.my.host/custom'"
     ],
     "name": "echo patch_repository_url"
   },
   {
     "cmd": [
       "echo",
-      "'properties:example'"
+      "'properties:examples/full'"
     ],
     "name": "echo recipe"
   },
   {
     "cmd": [
       "echo",
       "'chromium.testing.master'"
     ],
     "name": "echo mastername"
   },
@@ skipping 59 matching lines @@
       "'test_bot'"
     ],
     "name": "echo bot_id"
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]