python:tests: make test_export_keytab_nochange_update() more reliable

python:tests: make test_export_keytab_nochange_update() more reliable

net.export_keytab() includes the current timestamp into the resulting
keytab. So we need to make sure the two compared exports actually
run within the same second.

And klist may also print the keytab filename...

Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Andreas Schneider <asn@samba.org>
Autobuild-User(master): Stefan Metzmacher <metze@samba.org>
Autobuild-Date(master): Wed Jul 17 14:21:30 UTC 2024 on atb-devel-224