Use named-checkzone to check zonefiles for syntax-errors

[morgana2313]

The state bind.config doesn't check the contents of zone files with named-checkzone.

I would be nice to have this state fail on zones with errors in stead of exiting with "Succeeded", and to find with further investigation that bind didn't actually load the faulty zone because of errors.

[morgana2313]

And the same goes for checking the bind config with named-checkconf after making changes and before restarting bind.

[morgana2313]

named-check -z does both in one go.