During the upgrade from Mitaka to Newton, the uid/gid may change for the
same image. Especially on Ubuntu, we moved to Ubuntu Xenial in Newton
and it added systemd related user which break all the uid/gid during an
upgrade. It will the permissions in all docker named volumes.

This fix extends set_config.py to set the proper permission during
container start. This is super light then add commands in
extend_start.sh file  or add ansible tasks.

This patch just fixes rabbitmq case. Other services will be fixed in
following patches.

Partial-Bug: #1631503
Change-Id: Ib17027b97abbc9bf4e3cd503601b8010325b5c5b