KRB5: use given host name instead of reverse lookup'ed name

KRB5: use given host name instead of reverse lookup'ed name

This code would previously use dns_entry->addr->ai_canonname
instead of the given host name, which caused us grief and
problems since not all our resolver options do the reverse lookup
and I would also guess that it caused problems with KRB5/GSS with
virtual name-based hosts. Now the host name from the URL is used.