OS-479, DHCP service workflow fixes

    * dhcp_members was asigned but infoblox services wasnt restarted
    * dns server wasnt assigned in infoblox DHCP service
Merge pull request #13 from Vegasq/OS-479

OS-479, DHCP service workflow fixes
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