Enable EPEL repository for CentOS amphorae
Enable EPEL repository for CentOS amphorae

This is needed to install the package 'jq'

Not needed for other Red Hat variants:
* Fedora has jq in its main repo
*  RHEL has it in OpenStack repos (required to build a RHEL amphora)

Change-Id: I5c1c911c28215410b7f4c984bee8a69f0bee43eb
Closes-Bug: #1640827

openstack/octavia,openstack/octavia,openstack/octavia