Fixs dockerfile tests that did not work

tests/dockerfile/binder-dir/binder/Dockerfile

@@ -1,6 +1,12 @@
 FROM python:3.5
 
-ENTRYPOINT "/bin/sh"
+RUN pip install --no-cache notebook
+
+CMD "/bin/sh"
 
 ADD sayhi.sh /usr/local/bin/sayhi.sh
 ADD verify verify
+
+ARG NB_UID
+ENV HOME /tmp
+USER $NB_UID

tests/dockerfile/binder-dir/verify

@@ -1,3 +1,3 @@
-#!/bin/sh
+#!/bin/bash
 set -euo pipefail
 /usr/local/bin/sayhi.sh

tests/dockerfile/simple/Dockerfile

@@ -1,6 +1,12 @@
 FROM python:3.5
 
-ENTRYPOINT "/bin/sh"
+RUN pip install --no-cache notebook
+
+CMD "/bin/sh"
 
 ADD sayhi.sh /usr/local/bin/sayhi.sh
 ADD verify verify
+
+ARG NB_UID
+ENV HOME /tmp
+USER $NB_UID

tests/dockerfile/simple/verify

@@ -1,3 +1,3 @@
-#!/bin/sh
+#!/bin/bash
 set -euo pipefail
 /usr/local/bin/sayhi.sh