cephx key management fixes

 * place admin keyring in /etc/ceph (fixes Nova failure to attach a
   Ceph-backed volume to a VM)
 * consistently parametrize pools, Cephx users and ACLs
 * use parametrized Cephx user when generating Nova secret
 * unscatter creation of Cinder and Glance pools into ceph::pool
 * stricter ordering for creating pools and configuring backends for
   Cinder and Glance