The ceph-agent role was used only for RHCS 2 (jewel) so it's not
usefull anymore.
The current code will fail on CentOS distribution because the rhscon
package is only avaible on Red Hat with the RHCS 2 repository and
this ceph release is supported on stable-3.0 branch.

Resolves: #4020

Signed-off-by: Dimitri Savineau <dsavinea@redhat.com>
(cherry picked from commit 7503098ca079b200b3adcb1faf2e255d9c74a581)