When training, cannot specify filename for myconfig.py

[cfox570]

I create a set of config files for different purposes. I can specify myconfig filename when running manage.py but not when training.

[Ezward]

I like this idea. One of the most common issues we have is having different configuration when training on the laptop than we have when driving with the donkeycar. We might even want to require the user to specify a myconfig.py when training; that would make them conscious of the issue.

[DocGarbanzo]

I already have the change in one of branches, it's really small, hopefully I'll get to it in the next days.

[DocGarbanzo]

Addressed in #997