Enable natresolver and natdnsproxy for vagrant.

There are cases where tests run will fail when trying to download
from the outside world due to dns issues. In order to resolve this
I configured the natdnsproxy1 and natdnshostresolver1 vagrant settings
(gh-470) refactoring natdns to use the unless syntax
Merge pull request #422 from liamjbennett/vagrant_natdns

Enable natresolver and natdnsproxy for vagrant.