Pull etag from parsed response, not http headers

This was working around a botocore bug, but it's now fixed
in botocore so this workaround isn't needed.
Remove httpretty as a test dep

Instead we patch things out at the botocore level,
specifically botocore.endpoint.Endpoint.make_request.
Remove unused imports
Remove httpretty from requirements.txt
Merge branch 'no-httpretty' into develop

* no-httpretty:
  Remove httpretty from requirements.txt
  Remove unused imports
  Remove httpretty as a test dep
  Pull etag from parsed response, not http headers

Conflicts:
	requirements.txt