test: check non-root shared mounts

The idea of this test is to check non-root shared mounts
which lives in a few shared groups.

v2: fix the link description.

travis-ci: success for test: check non-root shared mounts (rev2)
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>