Add admin only action for force detach

Add admin only action for force detach

This action calls the same methods nova would after it successfully
detaches a volume.  By exposing it to the administrator it makes it's
easier to repair un-syncronized state between services.  Generally when
the host is no longer attached, but the volume state is wrong.

Future work: The Iscsi based drivers don't seem to use
initialize_connection and terminate_connection to create the export for
the volume.  This would be more useful with drivers that do that.

I added the force parameter to terminate_connection for drivers that may
want to differintiate between a normal terminate and the force detach.

Future Nova work:  Nova will want an admin action to update the bdm
tables - today it's a bit of nova-manage shell work.

Change-Id: Icc1cff0f50a5ace9ebdae62c85524ee8d6ec23e0