Feature config file path cli arg

Allow specifying server side config.json path as a cli argument

This is mostly useful for developers I guess. I use the same code on my
ubuntu box, and share it to my win7 virtualbox. This was the easiest way
I could think of.

I need to have different path replacements for both systems, as well as
test commands.

I don't know if I intended the older commit to be a part of this.
You can `cherry-pick` the other only into master if you see it fit better.