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.
Backout update to requests 2.0.0 for now because httpretty 0.7.0 is broken on Python 3.3.
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