$(hostname) is Ceph Monitor name in extend_start.sh,
{{ ansibe_hostanme }} is Ceph Monitor name in ceph.conf.
$(hostname) not always equal to ansible_hostname , that
makes ceph_mon container can't start.
Closes-Bug: #1538870
Change-Id: I312bf8d74c855aa4c72f12285e3092df96f60048