Comment 5 for bug 1667707

This happens because Twisted 13.2.0-1ubuntu1 in trusty has this transitional code:

    def listenUNIX(self, address, factory, backlog=50, mode=0o666, wantPID=0):
        assert unixEnabled, "UNIX support is not present"
        # Move this import back up to main level when twisted.internet.unix is
        # ported to Python 3:
        from twisted.internet import unix
        p = unix.Port(address, factory, backlog, mode, self, wantPID)
        p.startListening()
        return p

which means that the release-upgrader process will effectively import a mix of 13.2.0-1ubuntu1 and 16.0.0-1. Applying this diff to the current trusty landscape client should make the release upgrade succeed:

http://paste.ubuntu.com/24151525/