Implement Registry's Client V2

The patch implements Registry's v2 Client.

Some notes:
* The implementation uses __getattr__ to map method's calls to remote
  RPC methods.
* The client supports both bulk and single calls.
* Client is based on the base HTTPClient

About Exceptions:
* If raise_exc == True, the client will try to re-raise the remote
  exception. If the server raised an unknown exception, it will be
  re-raised as RPCException in the client side.

Implements blueprint registry-api-v2

Change-Id: I98757c2272c68301373c1a3af96c4d06cb63cc97
Merge "Implement Registry's Client V2"