Send fdb remove message when a port is migrated

the fdb_remove rpc message is sent when the status
of the port goes to BUILD, that is when the new host
send a get_device_details which means that it owns
the migrated port. The fdb_add message will be sent
as soon as the new host send update_device_up

Closes bug: #1237841

Change-Id: Ibdc7768d8db922b7e6eb9dc505382168cbb8e55d
Merge "Send fdb remove message when a port is migrated"