make: Add check-all target

The previous patch made it easy to skip the stress and slow tests, and
hard to run them. This make it easy again to run the stress and slow
tests:

    make check-all

Change-Id: I6ef034a8ca11473efcad3b568f4bb6df886b3ce6
Signed-off-by: Nir Soffer <nsoffer@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/32721
Reviewed-by: Dan Kenigsberg <danken@redhat.com>