'add an external_ip to the external_ips list'

def add_external_ips(self, inc_external_ips):

    if (not isinstance(inc_external_ips, list)):
        inc_external_ips = [inc_external_ips]
    external_ips = self.get_external_ips()
    if (not external_ips):
        self.put(Service.external_ips, inc_external_ips)
    else:
        external_ips.extend(inc_external_ips)
    return True
