[Update] Spark updated to 2.1.1

Revert "Fix sudoers.d inclusion on debian img (fix #394)"

This reverts commit 4b3b6697.

Add logs to start.sh

Fix sudoers.d inclusion with debian img (fix #394)

singleuser-start adjustments

Update Tensorflow example

Signed-off-by: Gaetan Semet <gaetan@xeberon.net>

Signed-off-by: Gaetan Semet <gaetan@xeberon.net>

DockerSpawner sets certain environment variables, so assume jupyterhub entrypoint when defined

ensures common behavior of things like GRANT_SUDO

Fix chown of $NB_USER home

finish removing files from $HOME

`initialize_all_variables` is deprecated, although it still works, and `global_variables_initializer` is the replacement.

- mplimporthook should be obsolete with matplotlib 2.0
- curlrc seems to be obsolete now (updates to base image?)
- set WORKDIR to $HOME instead of $HOME/work (leave work there for compatibility)

Change GID of NB_USER to NB_GID if NB_GID is passed as a parameter

install Julia packages in /opt/julia

reduce files in home directory a bit

singleuser: allow overriding port with JPY_PORT env

Add fonts-liberation requirement, fix #372

Updated patch file to build base-notebook Dockerfile on ppc64le