At present, cinder/nova/glance/gnocchi relative containers's
ceph.conf aren't be merge from user custom's config.
In some condition, we should add extra parameter to custom's
ceph.conf, for example:rbd_default_features = 1.
So, it is necessary to use merge_configs instead of template.
Closes-Bug: #1656162
Change-Id: I824e0c68af270b85c52382ae35987213266fc6f6