Add an authdns module & associated role classes

This adds an authdns module. The module is an uncommon for our tree
mixture of a role module, a package replacement (scripts) and internal
logic to handle the configuration of the authdns cluster. It serves as a
replacement to both dns.pp's authdns parts and the
wikimedia-task-dns-auth package, although both are significantly
rewritten.

A gdnsd module is not provided here, as the software is simple enough to
not warrant it (a single Package & Service definition).

This also adds role classes for each of ns0/ns1/ns2 (with their current
IPs) and a testns class for playing with in labs. These are all UNUSED
for now.

This is the initial work. Pending work includes adding IPv6 addresses,
switching to the commercial GeoIP databases and providing scripts for CI
integration. Plus, bug fixes :)

Change-Id: Ice119ead68bd7cb5a232f31c778b03791a917012
Merge "Add an authdns module & associated role classes" into production