launch single-user entrypoint if JUPYTERHUB_API_TOKEN is defined

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

base-notebook/start-notebook.sh

@@ -4,4 +4,9 @@
 
 set -e
 
-. /usr/local/bin/start.sh jupyter notebook $*
+if [[ ! -z "${JUPYTERHUB_API_TOKEN}" ]]; then
+  # launched by JupyterHub, use single-user entrypoint
+  exec /usr/local/bin/start-singleuser.sh $*
+else
+  . /usr/local/bin/start.sh jupyter notebook $*
+fi