Adds new typed param for migration and uses this as a UNIX socket path that
should be used for the NBD part of migration. And also adds virsh support.
Partially resolves: https://bugzilla.redhat.com/1638889
Signed-off-by: Martin Kletzander <mkletzan@redhat.com>
Reviewed-by: Jiri Denemark <jdenemar@redhat.com>