Prevents crash if an interface doesn't have an address
Fixes the mon_addresses refactor
Boolean functions should end in ?
Finds the primary ipv4 on mon nodes

Prevents issues with clustered IPs being used in ceph.conf files
Since ceph-mon doesn't bind to these ips, don't consider them as mon addrs
Merge pull request #110 from hufman/fix-interfaces-without-addresses2

Prevents crash if an interface doesn't have an address