Fix rabbitmq retry for error checking

I think this retry check has been broken since we introduced "set -e".
Unfortunately it seems the issue of rabbitmq not starting first-time
persists on centos 7 hosts occasionally, e.g. [1]:

---
 + rabbit_setuser stackrabbit secretrabbit
 + local user=stackrabbit pass=secretrabbit found= out=
 ++ sudo rabbitmqctl list_users
 Error: unable to connect to node 'rabbit@devstack-centos7-rax-iad-100675': nodedown

 DIAGNOSTICS
 ===========

 nodes in question: ['rabbit@devstack-centos7-rax-iad-100675']

 hosts, their running nodes and ports:
 - devstack-centos7-rax-iad-100675: [{rabbitmqctl29293,39511}]

 current node details:
 - node name: 'rabbitmqctl29293@devstack-centos7-rax-iad-100675'
 - home dir: /var/lib/rabbitmq
 - cookie hash: KieJnx1pnllKbHVihGcDqA==
---

Fix up this retry while we investigate [2]

[1] http://logs.openstack.org/64/141864/1/check//check-tempest-dsvm-centos7/4308f0c/logs/devstacklog.txt.gz
[2] https://bugzilla.redhat.com/show_bug.cgi?id=1144100

Change-Id: I11fb3728e08adc1e0f7acca63e5a308d24dce78e
Merge "Fix rabbitmq retry for error checking"
Merge branch 'master' of https://github.com/openstack-dev/devstack