Fix the rpc module import in the service module

After porting Nova to oslo.messaging, we forgot to change the import to
point to the new rpc module, and thus the rpc cleanup() method was never
called on service shutdown.

Change-Id: Ic06a19d9b9b98e1575d0aa72afa0d5ae71f6513a
Merge "Fix the rpc module import in the service module"