Also change CMD vs ENTRYPOINT to match what minimal-notebook
and some major official Docker images do (redis, mysql, nginx, ...)
by having the jupyter kernelgateway in the CMD, and just tini --
in the entrypoint
(c) Copyright IBM Corp. 2016
* Use setuptools to get modern pip (debian packaged pip stops
working after requests gets updated)
* Don't use wget to fetch tini, use Python!
(c) Copyright IBM Corp. 2016
* Remove SHELL env var and leftover USER nobody
* Install wget for tini then immediately uninstall it
* Install build-essentials and python3-dev for tornado speed up
then immediately uninstall them
(c) Copyright IBM Corp. 2016
