prepare for production use of 'donar' replacement.

This patch prepares the utility slice and the nodar dns shim for deployment to M-Lab.

 - use 'donar' in domain (rather than 'nodar' during testing)
 - uses 5 min TTL
 - adds explicit list of servers to initialize/start the dns service.

To be completed:
 - Deploy the slice to the servers listed in conf/donar.txt
 - Update the NS records on donar.measurement-lab.org for the global measurement-lab.org zone.