use "rabbit_hosts" config option instead of "rabbit_host"

This allows for easy client configuration against clustered RabbitMQ
setups.  Does not break existing configs.

Change-Id: I2b180f8860a727e35d7b465253689e5e8c44eb98
Closes-Bug: 1286411
Adds support for IBM SDN-VE Neutron plugin

This provides the support for the monolithic plugin
for IBM SDN-VE that is being added to Neutron here:
https://review.openstack.org/#/c/66453/

Implements: blueprint ibm-sdnve-plugin-support
Depends-On: I92619a95bca2ae0c37e7fdd39da30119b43d1ad6
DocImpact

Change-Id: I0958457355036fdab93156cd7fb4afd1a458918b
Merge "use "rabbit_hosts" config option instead of "rabbit_host""
Merge "Adds support for IBM SDN-VE Neutron plugin"
Merge branch 'master' of https://github.com/openstack-dev/devstack