Code review comment for lp://staging/~benji/landscape-client/bug-1428826-restore-register-function-public-API

I don't see how this change will make the charm work

Charm code hooks/common.py ~ line 171

            register(config, on_error=error_handler.flag_error)

This branch will fall over because there is no reactor being passed, the docstring suggests it should only be passed if you're doing crazy things, but it's a positional argument (!).