tests: allow [Errno] in output
I'm not sure why, but my system is printing "[Errno -5]" before
the "No address associated with hostname" message. I suspect a
modern version of Python improved errno tracking or something.
Add an "[Errno ...]" pattern as optional output to make the test
pass.
Differential Revision: https://phab.mercurial-scm.org/D1958
(binary:application/octet-stream)