zdtm: add flock file lock's test case

We check shared lock, exclusive lock and mandatory-read lock for flock
file locks. After restore, by parsing /proc/locks file, we check if
the process holds the same file locks as it was dumped.

Signed-off-by: Qiang Huang <h.huangqiang@huawei.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>