zdtm: Add unlink_regular00 test

Test checks that a deleted file content in a deleted parent directory
restores right. Initially directory is created in a separate mount,
to check the ghost file is created in right mount and link() in
rfi_remap() is working.

Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>