create /root/ceph.conf symlink on all ceph nodes

We need /root/ceph.conf to link to /etc/ceph/ceph.conf on all ceph nodes, not
just primary monitor. With ceph-deploy 1.3+, if Puppet modifies
/etc/ceph/ceph.conf and makes it differ from /root/ceph.conf (e.g. change host
for radosgw), all subsequent ceph-deploy commands will fail.

Change-Id: I6254c35f546cd22837d29e952b8632759d5b40f8
Closes-Bug: #1328881
Merge "create /root/ceph.conf symlink on all ceph nodes"