In certain circumstances the docker events process can be leaked and left running

[bwateratmsft]

I've been doing some experimentation and found that the docker events process started for #3674 can be "leaked" and left running. In normal VSCode shutdowns, the extension deactivates and the process is killed as expected. However, if I do "Reload Window", it seems that the deactivation pathway never occurs. The PowerShell process (on Windows) is killed properly, but the docker events process underneath it persists.

[bwateratmsft]

There's two potential solutions I can think of:

1. Use the --until flag to put a maximum lifetime on the docker events process
2. Don't run the process in a shell