Make our 'get DNS domain name' code try a bit harder - if gethostname() doesn't

Make our 'get DNS domain name' code try a bit harder - if gethostname() doesn't
include a domain portion, do a gethostbyname() lookup on that name.

Use this name in our PolicyPrimaryDomainInformation reply (_lsa_query_info2)
that Win2k uses when trying to trust us as a trusted domain.

(We need to do a better mapping between our Netbios and Win2k domain names,
but this will do for now - particularly annoying is the way this possibly needs
to map with our kerberos realm).

Andrew Bartlett
(This used to be commit 3be03271030208a69da29c6e2a7b92cdbaa8c6aa)