Use fqdn_ip4[-1] for ip address of [mon.a] in ceph state config.

While '$ salt minion network.ip_addrs' did return the ip address[es] from the command line, the old {{ salt['network.ip_addrs'][-1] }}, when using the [-1] offset, would cause Jinja 'undefined variable' errors (interestingly on the last instance of {{ grains['localhost'] }}); removing the [-1] offset allowed the state to pass, but the value of {{ salt['network.ipa_addrs'] }} compiled in the template as string "<function ip_addrs at 0x9d30a3c>", which I was not interested in exploring, and so decided to get the ip address this way.