memcg_test_3: don't send signal when parent unexpectedly exited

[ZhangHongchen1]

When the parent process exits abnormally for some reason, the parent process of the child process will become process 1. In this case, the child process should not send signal to process 1.

So we compare the realy parent pid and the saved parent pid,the child process should exit when they has mismatched.

Signed-off-by: Lingling Li [email protected] Signed-off-by: Hongchen Zhang [email protected]