Fix dynamic ipv6 address check & DNS tests

[rhxto]

I ran make tests and they all pass. The DNS issue is not reported because I ran into it while testing my changes. This is my first time contributing to anything open source, so I would love your feedback on this merge request : )

Fixes #877

PS: as cited in the issue, I ran into this while using ceph-osd. Manually changing the file like in this merge request fixed it.