In case of some services it makes much sense for caller to receive also
stderr in addition to stdout. For example:
- qubes.VMShell (stderr required for salt-ssh over qrexec)
- qubes.OpenInVM - especially when called to DispVM - otherwise
diagnosing errors can be hard
And generally all sort of error reporting (the purpose of stderr). It
would ease debugging - instead of message "error occurred, check here and
there for more details", it could be "error occurred: the reason".
FixesQubesOS/qubes-issues#1808
b267e5c305