Add a flag to rabbitmq so that we can deploy with ha-mode: all again

Add a flag to rabbitmq so that we can deploy with ha-mode: all again

In change Ib62001c03e1e08f58cf0c6e0ba07a8879a584084 we switched the
rabbitmq queues HA mode from ha-all to ha-exactly. While this gives us a
nice performance boost with rabbitmq, it makes rabbit less resilient to
network glitches as we painfully found out via
https://bugzilla.redhat.com/show_bug.cgi?id=1441635.

Will propose another THT change to actually change the default to
-1 so we get this ha-mode:all by default.

Change-Id: I9a90e71094b8d8d58b5be0a45a2979701b0ac21c
Partial-Bug: #1686337
Co-Authored-By: Damien Ciabrini <dciabrin@redhat.com>
Co-Authored-By: John Eckersberg <jeckersb@redhat.com>