Specify 'endpoint' param in mwerrors.pyconf

I left this out of I55450783d by mistake. This should ideally be a template
which interpolates a class parameter, but looking to fix things first before
getting fancy.

Change-Id: I0c079a1d869e49598a54db83eee71b8a390130f7
Merge "Specify 'endpoint' param in mwerrors.pyconf" into production