packaging: ship libdir/ceph

Automake puts ceph_common.sh into libdir/ceph, but the Red Hat packaging
was not capturing this file.

Add the libdir/ceph location to the RPM packaging.

Fixes #7117
Merge pull request #1094 from ceph/wip-7117-redhat

packaging: ship libdir/ceph

Reviewed-by: Sage Weil <sage@inktank.com>