zdtm: mount test cgroup controllers before executing tests

If a controller is mounted during dumping processes, criu may fail with error:
Error (cgroup.c:768): cg: Set 3 is not subset of 2

so lets create all test controllers before executing tests.

Reported-by: Mr Jenkins
Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>