s4:selftest: test for smbtorture subunit names with and without --fullname

s4:selftest: test for smbtorture subunit names with and without --fullname

We check the output with both --fullname and with the default shortname
to ensure it works as expected.

We also do tests for each level and test relative names are used.

Pair-Programmed-With: Stefan Metzmacher <metze@samba.org>

Signed-off-by: Sachin Prabhu <sprabhu@redhat.com>
Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Andreas Schneider <asn@samba.org>
Autobuild-User((no branch)): Stefan Metzmacher <metze@samba.org>
Autobuild-Date((no branch)): Tue Jul  7 12:16:34 UTC 2020 on sn-devel-184