SSH virsh to use the new ManagementInterface

Add the new ManagementInterface to the SSH driver. Only the 'virsh'
virt_type is supported for now.

Implements: blueprint new-management-interface
Change-Id: I36b704e4d9daa902393b3f79405bf288d9ee0872
Update_port should expect MACAlreadyExists

Conductor manager's update_port() method should include
exception.MACAlreadyExists in the list of expected exceptions.  This
will stop logging it as a traceback on the Conductor when a client
attempts to update a port and change its address to one that is already
registered.

Change-Id: Ic575e03da566c7b44bf6b72ac171633d80165ffc
Closes-Bug: #1348676
Merge "Update_port should expect MACAlreadyExists"
Merge "SSH virsh to use the new ManagementInterface"