Simple implementation of DNSMasq backend

The logic is quite simple. All dns zones are stored in separate files.
They are eventually merged into one flat dns zone.
And this file (or any separate zone) should be specified in dnsmasq config file (--addn-hosts=).
Update is also simple, all you need is to send a SIGHUP to dnsmasq to force re-read of the file.

Change-Id: Id634ca2843fd02a8406913881d4989c7c2112249
Wrap backend interactions in try/catch blocks

Change-Id: I3e4e3b9a8ace7cd89d2244aca07248e7cfaaad9d
Merge "Simple implementation of DNSMasq backend"