Comment 2 for bug 1606203

Looks like bzr has trouble talking to the Launchpad directory service through an authenticated proxy (it's getting a bit confused and using the proxy credentials in the wrong place), which is at least arguably a bzr bug. That will probably be no fun to fix, and there's not much activity on bzr at the moment, so it may be most economical to hack snapcraft to unset https_proxy when calling bzr, with a comment explaining that this is due to this bug.