fix-3942: keyboard interrupts & stdout

[DavidBord]

Since initial imports are pretty slow a keyboard interrupt generates a pretty nasty traceback to stdout so suppress them until the logger that deals with it is initialized

Fixes #3942

[cjerdonek]

I’m not sure we want to be suppressing the default signal handler as tracebacks are useful for understanding e.g. where pip got stuck. Also, the original issue was about auto-completion and suggested a narrower fix.

[pfmoore]

Agreed, I think this is too broad a change to be appropriate as a fix for #3942, which is a very specific problem.

[auvipy]

How can I cancel my review?

[pradyunsg]

We spent a while discussing this at PyCon (me and @DavidBord). I think we should take a step back and the fix for this would probably be just to suppress stderr when pip's being used for autocompletion -- this would be a change in our completion scripts defined in autocompletion.py.