zdtm: use a separate file for flock

In Ubuntu flock opens a file with O_RDWR and then it can't be executed
flock: ./zdtm_mount_cgroups: Text file busy
Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>

test/zdtm.py

@@ -432,7 +432,7 @@ class zdtm_test:
 			subprocess.check_call(["make", "zdtm_ct"])
 		if not os.access("zdtm/lib/libzdtmtst.a", os.F_OK):
 			subprocess.check_call(["make", "-C", "zdtm/"])
-		subprocess.check_call(["flock", "zdtm_mount_cgroups", "./zdtm_mount_cgroups"])
+		subprocess.check_call(["flock", "zdtm_mount_cgroups.lock", "./zdtm_mount_cgroups"])
 
 
 class inhfd_test: