Clean the "CentOS" branch, so that it should work for all CentOS/RHEL variants (7.x). Make sure to install the required repositories also in the non-Manila case. Fedora already ships Ceph packages so does not need additional repositories. Do not try to install ceph-radosgw twice. Finally, explicitly fail for other distributions (not supported de-facto even in the current code). Change-Id: I83b1fffad405bc122bc55ef1173f5239f41d2b36