testprogs: Add 'net ads join createupn' test also verifying the keytab

testprogs: Add 'net ads join createupn' test also verifying the keytab

BUG: https://bugzilla.samba.org/show_bug.cgi?id=14336

Signed-off-by: Andreas Schneider <asn@samba.org>
Reviewed-by: Alexander Bokovoy <ab@samba.org>
Autobuild-User(master): Andreas Schneider <asn@cryptomilk.org>
Autobuild-Date(master): Mon Apr  6 19:09:53 UTC 2020 on sn-devel-184

(cherry picked from commit c4be195da2845be4f64e47883e3c911dedd90e48)

Autobuild-User(v4-12-test): Karolin Seeger <kseeger@samba.org>
Autobuild-Date(v4-12-test): Tue Apr  7 09:36:45 UTC 2020 on sn-devel-184