remove yum priority
remove yum priority

In the past we were using priority in order to mask package from epel.
now we only install epel with a very limited list of allowed pkg and only when
needed. This patch remove the priority for yum repos.

Change-Id: Ic6525e013b96e00d115d13a2b9e8fb00c3000127

openstack/openstack-ansible-pip_install,openstack/openstack-ansible-pip_install