don't create js test directories unless they are being used

just moves a setup block from `__init__` to `launch`
Merge pull request #5083 from minrk/one-nb-server

don't create js test directories unless they are being used
Updating JS tests README.md.
Merge pull request #5078 from ellisonbg/js-readme

Updating JS tests README.md
Merge remote-tracking branch 'upstream/master'