Support cloudsearchdomain service

In addition to adding the JSON model,
there are also a few fixes required:

* Support streaming uploads for rest-json service
* Don't raise an exception if endpoint heuristics fail to
  find anything but a endpoint_url is given
Update cloudfront model to the latest version
Bumping version to 0.54.0
Merge branch 'release-0.54.0' into develop

* release-0.54.0:
  Bumping version to 0.54.0
  Update cloudfront model to the latest version
  Support cloudsearchdomain service