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

tests/test-clonebundles.t

@@ -53,7 +53,7 b' Manifest file with invalid URL aborts'
   $ echo 'http://does.not.exist/bundle.hg' > server/.hg/clonebundles.manifest
   $ hg clone http://localhost:$HGPORT 404-url
   applying clone bundle from http://does.not.exist/bundle.hg
-  error fetching bundle: (.* not known|No address associated with hostname) (re) (no-windows !)
+  error fetching bundle: (.* not known|(\[Errno -?\d+])? No address associated with hostname) (re) (no-windows !)
   error fetching bundle: [Errno 11004] getaddrinfo failed (windows !)
   abort: error applying bundle
   (if this error persists, consider contacting the server operator or disable clone bundles via "--config ui.clonebundles=false")