Ive made a few changes to your excellent role, to get it working for my company, so thought id push them back upstream.

This is my first ever pull request btw :). 

1. Validate for the zone db files
2. Cleaned up tasks.yml;
    a. made some tasks multi-line to fit better on standard terminals
    b. changed an action: to template:
    c. added ability to sync include files
    d. The above would have --chown: {{ bind_user }}:{{ bind_group }} but this needs rsync 3.1 so only recent ubuntu/Debian compat
       so added workaround chown task
3. Added default DNS forwarders to Google DNS (so it works out the box if you don't specify one)
4. Added recursion option so bind can function as a cache server