'Returns a list of moved ports.
Takes two port->ofport maps and returns a list ports that moved to a
different ofport. Deleted ports are not included.'

@staticmethod
def _get_ofport_moves(current, previous):

    port_moves = []
    for (name, ofport) in previous.items():
        if (name not in current):
            continue
        current_ofport = current[name]
        if (ofport != current_ofport):
            port_moves.append(name)
    return port_moves
