Replace NSX bridge cluster with bridge endpoint profiles as the
backend resource used to implement L2 gateways.
The logic for creating a gateway connection is not changed,
with the only exception that bridge endpoints now have a reference
to a bridge endpoint profile.
Connections created using bridge clusters can be safely removed,
while creation of new connection on gateways leveraging bridge
clusters will fail.
Change-Id: I29cd9a2501ab4b7dd226729f33ab962bbba2dfff
0a952ce786