Add a new 'outward' rabbitmq instance

Certain services such as Murano and trove require access to a rabbitmq
instance from tenant networks. [0]

Exposing the internal rabbitmq to end users is a security hole, hence
there are two options, 1) use vhosts in the existing rabbitmq, or two a
separate rabbitmq instances. Given the importance of rabbitmq to the
OpenStack deployment, we have decided to go with a separate instance.
Refer to [1] for more detail on the various options.

This change makes the rabbitmq role generic so that it can be reused, in
this case to start 'outward_rabbitmq'. It needs to be exposed via
haproxy both for network isolation and also because this is what Murano
configuration requires.

Follow on patches will be added to add a vhost in this outward instance
for Murano and other services which require access.

Based on the original work by bdaca[2]

[0] http://murano.readthedocs.io/en/stable-liberty/intro/architecture.html
[1] http://lists.openstack.org/pipermail/openstack-dev/2016-December/109091.html
[2] https://review.openstack.org/#/c/374525



Change-Id: Ib2bcc7ed4bf4f883a7cd1dfad3db89201e3cfd8d
Partial-Bug: #1620374
Depends-On: I020eb6219f89a310451becde41f6f1c7f54baadd
Co-Authored-By: Bartłomiej Daca <bartek.daca@gmail.com>