HA Docs: Document RabbitMQ in Active / Active setup
HA Docs: Document RabbitMQ in Active / Active setup

This is the first commit of active / active section for RabbitMQ
in the OpenStack HA guide.

bug #1196097
Blueprint improve-high-availability-support

Change-Id: I5d0a0c6849974b62ba18d785eff393674f86b4fb

kairoaraujo/openstack-manuals,openstack/openstack-manuals,AlekhyaMallina-Vedams/openstack-manuals,kairoaraujo/openstack-manuals,openstack/openstack-manuals,openstack/openstack-manuals,potsmaster/openstack-manuals,saeki-masaki/openstack-manuals,Akasurde/openstack-manuals,AlekhyaMallina-Vedams/openstack-manuals,gongysh2004/openstack-manual,gongysh2004/openstack-manual,saeki-masaki/openstack-manuals,AlekhyaMallina-Vedams/openstack-manuals,openstack/openstack-manuals,potsmaster/openstack-manuals,Akasurde/openstack-manuals