Test creates two shared mounts, both are readonly, on each mount we have
a different ghost file. Also let these mounts have different mount
flags. That makes us both test do_new_mount hunk for delaying readonly
and do_bind_mount, as one mount will bind from another on restore.

https://jira.sw.ru/browse/PSBM-82991

v2: minor cleanup
Signed-off-by: Pavel Tikhomirov <ptikhomirov@virtuozzo.com>
Signed-off-by: Andrei Vagin <avagin@gmail.com>