zdtm: check an exit code of a straced restore

Currently zdtm doesn't detect when restore failed, if it is executed
with strace. With this patch, fake-restore.sh creates a test file, and
zdtm is able to distinguish when restore failed.
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>

scripts/fake-restore.sh

@@ -8,6 +8,7 @@
 # criu restore <options> --action-script $(pwd)/scripts/fake-restore.sh
 #
 if [ "$CRTOOLS_SCRIPT_ACTION" == "post-restore" ]; then
+	touch restore-succeeded
 	exit 1
 else
 	exit 0

test/zdtm.py

@@ -959,7 +959,8 @@ class criu:
 				grep_errors(os.path.join(__ddir, log))
 				if ret == 0:
 					return
-			if self.__test.blocking() or (self.__sat and action == 'restore'):
+			rst_succeeded = os.access(os.path.join(__ddir, "restore-succeeded"), os.F_OK)
+			if self.__test.blocking() or (self.__sat and action == 'restore' and rst_succeeded):
 				raise test_fail_expected_exc(action)
 			else:
 				raise test_fail_exc("CRIU %s" % action)