some execs that remain and do not exit

[xzchaoo]

Describe this problem

For unknown reasons, there may be some execs that remain and do not exit.
I think we need to have some means to prevent arbitrary execs from hanging permanently.

Steps to reproduce

This problem is not easy to reproduce.
It is very likely that holoinsight-agent exited abnormally while tar was reading data from STDIN, causing STDIN to be unable to read EOF for a long time, so it hung.

Expected behavior

No exec remains.

Additional Information

There are several ideas:

• Always use timeout to wrap all commands, and KILL when timeout occurs. But be aware that timeout can generate zombie processes in some scenarios. See #99
• All exec commands carry special environment variable tags to indicate that they are calls from holoinsight-agent. Periodically clean up processes that need to be marked. See utils.go

No response