selftest: Improve connection between primary domain and subdomain for krb5

selftest: Improve connection between primary domain and subdomain for krb5

Two things help here: The join is done on the lower case name, so we
can match it in the krb5.conf, and we share the krb5.conf between the
"dc" environment and the "subdom_dc" environment.  Between these two
measures, this means we can get tickets using the domain trust.

If we used cwrap for DNS queries and we had our internal DNS set up correctly,
we could avoid this (because that is not case sensitive),
but otherwise we need to get SUB.samba.example.org into the krb5.conf,
and this is harder to do an a generic way.

Andrew Bartlett

Change-Id: If378915112728aaf47aa68ce0b071a7e09d756ad
Signed-off-by: Andrew Bartlett <abartlet@samba.org>
Reviewed-by: Stefan Metzmacher <metze@samba.org>
Reviewed-By: Jelmer Vernooij <jelmer@samba.org>