Add RabbitMQ and QPID HA support flags to quantum.conf

Since Quantum supports HA queues with RabbitMQ (https://review.openstack.org/#/c/13760/),
quantum.conf should provide new flags for explain how to configure multiple RabbitMQ servers and enable HA.

New flags :
rabbit_hosts=$rabbit_host:$rabbit_port
rabbit_ha_queues=false
qpid_hosts = localhost:5672

Fix Bug #1160369

Change-Id: I35903b1b7b66fde8d70ac7e8076e0def2a1f2d04
Merge "Add RabbitMQ and QPID HA support flags to quantum.conf"