Make fabric-crossconnect service compatible with ONOS 1.5 and later

Currently the json format that fabric-crossconnect service uses to add Xconnect rules from ONOS REST would be

{     "deviceId": "of:0000000000000201",     "vlanId": "94",     "ports": [1, 2] }

However, ONOS 1.15 and later replaced `port` field to `endpoints`, which causes synchronization of fabric-crossconnect failed.

Please check https://github.com/opencord/fabric-crossconnect/blob/master/xos/synchronizer/steps/sync_fabric_crossconnect_service_instance.py#L134