(CFACT-41) Use resolv.conf for domain name fact resolution.

If we can't resolve the hostname, look for domain and search entires in
/etc/resolv.conf.

This allow us to conform to what facter is doing even when the hostname
is not resolvable.
Merge pull request #67 from peterhuene/cfact/41

(CFACT-41) Use resolv.conf for domain name fact resolution.