The openstack queens repo includes a contentdir var. This variable may
not be present in all systems. For our purposes this var should be
centos, so we will use that in place of the variable in the repo file.
See https://review.openstack.org/#/c/568180/
and
https://lists.centos.org/pipermail/centos-devel/2018-March/016542.html
Change-Id: Ie9314d0dfb20e6372ab6ca44ee38a67bfb85dd7c
Story: 2002845
Task: 22793
Signed-off-by: David Sullivan <david.sullivan@windriver.com>