OS-181 Add IP address for existing DNS record

Code silently rewrites DNS record for a given IP address if the DNS name
matches existing one. Rework so that IP address is added to existing DNS
name.

Change-Id: I41484c63adeb4910ecde967d30a1a8e8b54475ea
Merge pull request #36 from Vegasq/OS-181

OS-181 Add IP address for existing DNS record