Openbazaar python launcher

new pull request after 1st round of reviews.
Thanks @Renelvon this has the merged changes from your repo.

(@Renelvon I kept that REVERT commit you put there as I'm not sure I understood what was right or wrong about it, I figured it'd be easier to fix here now)
This method doesn't really make sense. Right now it is only used by the launcher which creates a new process in this method. Afterwards this method starts a number of nodes. Why can't we make the launcher start all the needed processes right away? And it would really make sense to make the launcher just call start_node without creating any new procceses at all when we only want to start a new process.