selftest: change technique for running specific envs

selftest: change technique for running specific envs

Currently testsuites excluded with --exclude/--include-env are skipped when
encountered in the middle of a run, so they are included in progress reporting,
and the @todo list does not accurately show what will be done.

This change skips them earlier, preventing them from being added to @todo, as is
done with pattern-based including/excluding.

As well as making the progress indicator more accurate, this means that
selftest.pl can use @todo to determine when we are finished with an environment.

Signed-off-by: Jamie McClymont <jamiemcclymont@catalyst.net.nz>
Reviewed-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>
Autobuild-User(master): Andrew Bartlett <abartlet@samba.org>
Autobuild-Date(master): Wed Feb 21 07:47:58 CET 2018 on sn-devel-144