Move packages section earlier

For SLES, RabbitMQ is part of the OpenStack repo, we thus need to
setup the Havana repository first before we can install RabbitMQ.

Closes-Bug: #1241190
Backport: stable/havana
Cherry-Picked from: https://review.openstack.org/#/c/52489/

Change-Id: I060606326134449cf582549fa68fa26f61171b75