Big Switch: Add missing data to topology sync

Adds data to the topology sync function that was
missing in the case where it is called from the
ML2 driver.

Closes-Bug: #1328222
Change-Id: I1cc3b0430f63f62c881f28139d1e5ebf22766357
Introduce RpcCallback class

This class will be used to create proper self.target with appropriate
API version once we migrate to oslo.messaging.

blueprint oslo-messaging

Change-Id: I1fb5eb0aaac0d115fd84630e58b333e695ad4f5f
Merge "Big Switch: Add missing data to topology sync"
Merge "Introduce RpcCallback class"