Update MGMT switch name
Update MGMT switch name

The virtual switch for the management communication is named MGMTSWITCH
instead of MGMT.  This updates the logic in nova-powervm to reflect
this.

Change-Id: Iee1f8b22c22c2f072da42b7d75ddea417397d444

stackforge/nova-powervm,openstack/nova-powervm,openstack/nova-powervm,stackforge/nova-powervm