Currently we skip all userns tests if "criu check" fails. This code was
written when the "freature" options of criu check didn't exist.

Currently we add userns tests only if "criu check --feature userns" passes.
Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>