reload zones when they are updated

[crispygoth]

Simply adds an exec resource to nsd::zone that runs nsd-control reload zonename whenever Puppet updates the file or the nsd::zone resource is a target of a notify/subscribe relationship.

[coveralls]

Coverage remained the same at ?% when pulling 6c4c1e7 on crispygoth:reload_zone_when_updated into 8f61a4c on bodgit:master.

[bodgit]

This possibly needs to require the service class being up otherwise I'm guessing it will error if nsd-control can't contact the main nsd process on a clean install.

Alternatively, add whatever exit code nsd-control returns when nsd isn't running to the accepted list of error codes. If nsd isn't yet running then it's going to (re)load all of the zones anyway when it starts.