Create peer router port in appropriate port driver function

Bug 1204288

Removes peer port creation from add_router_interface.
Also fixes port_drivers dict which had a duplicate key.
In addition clears attachment on the NVP logical switch part
being paired with the logical router port before plugging
the patch attachment.

Change-Id: I336b29bdf017b2d34d97412fbe034845fe314fc7
Merge "Create peer router port in appropriate port driver function"