Make subimages compatible with late user creation

* Always remain as root during install
* Put kernel specs in system path, not user home
* Create user work directory at startup
* Note this is in 4.0 and up images, not 3.2

Contribution (c) Copyright IBM Corp. 2015

minimal-notebook/start-notebook.sh

@@ -1,4 +1,5 @@
 #!/bin/bash
+set -e
 
 # Create non-root NB_USER, member of group "users"
 useradd -m -s /bin/bash -u ${NB_UID:-1000} -G users $NB_USER
@@ -7,6 +8,11 @@ useradd -m -s /bin/bash -u ${NB_UID:-1000} -G users $NB_USER
 chown -R root.users $CONDA_DIR
 chmod -R g+w $CONDA_DIR
 
+# Setup a work directory rooted in the NB_USER home
+mkdir -p $WORK
+chown root.users $WORK
+chmod g+w $WORK
+
 # Enable sudo if requested
 if [ ! -z "$GRANT_SUDO" ]; then
     echo "$NB_USER ALL=(ALL) NOPASSWD:ALL" > /etc/sudoers.d/notebook