Prefer IP addresses over hostnames

[s-urbaniak]

What version of the project are you using?
b8922a4

What operating system and processor architecture are you using?
OSX/amd64

What did you do?
I started a 1-zookeeper/3-mesos-master/1-mesos-dns testbed as described in #276 (comment).

I issued an A-record query:
$ dig @127.0.0.1 -p 5253 master.mesos +short A

What did you expect to see?
I expect to get the complete list of master IPs:

127.0.0.2
127.0.0.3
127.0.0.4

What did you see instead?
I get only one IP address:

127.0.0.2

[s-urbaniak]

xref #276