Comment 9 for bug 1573030

Reviewed: https://review.openstack.org/314458
Committed: https://git.openstack.org/cgit/openstack/openstack-ansible/commit/?id=0861feaf36bf2f1f6c52a8587cbf2b2dcbade65e
Submitter: Jenkins
Branch: stable/mitaka

commit 0861feaf36bf2f1f6c52a8587cbf2b2dcbade65e
Author: Darren Birkett <email address hidden>
Date: Thu May 5 22:17:11 2016 +0100

    install rabbitmq-server in serial

    In order to prevent race conditions with nodes joining the cluster
    simultaneously when the cluster is first formed, we move the rabbitmq
    installation play to be 'serial: 1'. However, when the nodes are being
    upgraded, it cannot be done in serial so in this case we set 'serial: 0'

    There are some tasks/roles called in this playbook that can still be
    run in parallel, so we split out the rabbitmq-server install into a
    separate play so that we only serialise the parts that are necessary
    to ensure maximum efficiency.

    Change-Id: I97cdae27fdce4f400492c2134b6589b55fbc5a61
    Fixes-Bug: #1573030
    (cherry picked from commit 21c24789019bf1ee85347356fe6c70b0b9045d7c)