Add Extensions to the v2 API

*Provide a framework for adding extensions to the v2 API.
*Port the Quotas extension
*Add v2 extension unit tests
*Fix small bug with noauth middleware and quota retrieval

blueprint v2-extensions
Closes-Bug: #1333892
Change-Id: I1dc395e7266a17c8c860e00ee470e14e94e82769
Merge "Add Extensions to the v2 API"