Don't add None responses to multi result key pagination

Also, switch from defaultdict to just creating the keys
with empty lists up front.  This is because now, even if one
of the result keys is always None, we still should have a top level
result key that's just an empty list, which wouldn't happen if we
were using a defaultdict.
Merge branch 'build-full-result-fix' into develop

* build-full-result-fix:
  Don't add None responses to multi result key pagination
Honor flattened attribute in model for rest-json
Fix test to not depend on inner xml order
Use a patched os.environ in tests

Don't use global state (os.environ) as this messes with tests.
Instead use the BaseEnvVar class that patches out os.environ for you.
This was causing a test fail because a test was depending on os.environ
being patched to have the access/secret key env vars available.
Merge branch 's3-flattened-fix' into develop

Closes #67

* s3-flattened-fix:
  Use a patched os.environ in tests
  Fix test to not depend on inner xml order
  Honor flattened attribute in model for rest-json
Fix whitespace to be consistent with JSON models.
Merge branch 'lsegal-fix-extra-json-whitespace' into develop

Closes #68.

* lsegal-fix-extra-json-whitespace:
  Fix whitespace to be consistent with JSON models.
Merge remote-tracking branch 'upstream/develop' into develop
Adding an example_fn attribute to Parameter object.