(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.
I was considering putting it to an INFO level since we're warning+ by default.  Even though it's nice to know your machine's hostname can't be resolved, it's probably a little too common to be treated as a warning.  Thoughts?