Comment 1 for bug 1729213

in function as follow:
 def get_or_create_ofport(self, port):
        """Get ofport specified by port['device'], checking and reflecting
        ofport changes.
        If ofport is nonexistent, create and return one.
        """
        port_id = port['device']
        ovs_port = self.get_ovs_port(port_id)

libvirt will delete tap when removed vms .then, ovs agent check ovs_port by "self.get_ovs_port" , and the exception will be raised.