eg https://circleci.com/gh/snarfed/bridgy-fed/164
```
testutil_appengine (unittest.loader.ModuleImportFailure) ... ERROR
...
======================================================================
ERROR: testutil_appengine (unittest.loader.ModuleImportFailure)
----------------------------------------------------------------------
ImportError: Failed to import test module: testutil_appengine
Traceback (most recent call last):
File "/usr/lib/python2.7/unittest/loader.py", line 254, in _find_tests
module = self._get_module_from_name(name)
File "/usr/lib/python2.7/unittest/loader.py", line 232, in _get_module_from_name
__import__(name)
File "/tmp/oauth-dropins/oauth_dropins/webutil/testutil_appengine.py", line 4, in <module>
from google.appengine.datastore import datastore_stub_util
File "/usr/lib/google-cloud-sdk/platform/google_appengine/google/appengine/datastore/datastore_stub_util.py", line 69, in <module>
from google.appengine.datastore import datastore_stub_index
File "/usr/lib/google-cloud-sdk/platform/google_appengine/google/appengine/datastore/datastore_stub_index.py", line 45, in <module>
import yaml
ImportError: No module named yaml
```
Ryan Barrett