include agent protocol in topic (MQTT)

[AlvaroVega]

twin issue telefonicaid/iotagent-ul#287

Currently topics used by iotagent-json and iotagent-ul are the same.
//<device_id>/attrs
There is no way to know if a topic (MQTT) is for UL or JSON agent.

Topic is fixed in agent source code:

https://github.com/telefonicaid/iotagent-json/blob/master/lib/bindings/MQTTBinding.js#L45
https://github.com/telefonicaid/iotagent-ul/blob/master/lib/bindings/MQTTBinding.js#L46

Topic is knowed by ACL files:

https://github.com/telefonicaid/iotagent-node-lib/blob/master/docker/Mosquitto/aclfile#L3
https://github.com/telefonicaid/rabbit-topic-acl/blob/master/docker/aclfile#L2

Possible solution: extending topics

/<protocol>/<apikey>/<device_id>/attrs

but is not backward compatible

[fgalan]

Implemented in PR #450

Can this issue be closed? Or is there anything pending?