test: don't execute cgroup03 with other cgroup tests concurrently

https://github.com/xemul/criu/issues/253
travis-ci: success for test: don't execute cgroup03 with other cgroup tests concurrently
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>

test/zdtm/static/cgroup03.desc

-{'flavor': 'h', 'flags': 'suid', 'opts': '--manage-cgroups'}
+{'flavor': 'h', 'flags': 'suid excl', 'opts': '--manage-cgroups'}