Ignore psutil exceptions in _find_agent.

[peter50216]

Fix #201.
When there's zombie process in system or some process disappears before listing and getting attributes, methods on proc would raise psutil.Error, and the import gnupg statement would fail.

[phryk]

Hey Peter. I don't know nearly enough about the architecture of this module to gauge whether it's wise to ignore all psutil errors. Maybe psutil.ZombieProcess or psutil.NoSuchProcess would be a more fitting exception to catch?

[peter50216]

Since the _find_agent function is run at import time, I still think we should ignore all psutil exceptions.
To me, it feels worse that import failed due to status of other process than not finding the right gpg-agent.
Also according to document, there are only three exceptions NoSuchProcess, AccessDenied, TimeoutExpired that are psutil.Error. (ZombieProcess is subclass for NoSuchProcess)
TimeoutExpired shouldn't be raised here, and I guess we'll want to ignore AccessDenied too.

[mdsn]

Bumping this PR. Is there further work that needs to be done for it to be merged? Thanks.

[msheiny]

Yeah we also independently ran into this issue, implemented the same fix, was about to make a PR and then saw this ticket 👍

[isislovecruft]

Hi @peter50216! Thank you for the patch, and I'm very sorry for the delays in reviewing it and getting it merged.

[isislovecruft]

I think I'd prefer to log when these errors occur, just in case, so that it doesn't silently cause something else to fail in some edge case in the future. I'm happy to make that change myself after merging your patch.

[isislovecruft]

Merged and in version 3.0.1.