adapt dir permissions for openshift and add dumb-init

This commit updates directory permissions to be compatible with
OpenShift which starts the container with an arbitrary uid which is
member of the root group. For more information please consult
https://docs.openshift.org/latest/creating_images/guidelines.html.

dumb-init is added to have a proper PID 1. bash should not run as PID 1
as this could lead to improper container shutdown.

Dockerfile

@@ -16,6 +16,12 @@ RUN cd /usr/bin && \
     tar -xf dockerize.tar.gz && \
     rm dockerize.tar.gz
 
+# dumb-init for a proper PID 1
+RUN cd /tmp && \
+    wget https://github.com/Yelp/dumb-init/releases/download/v1.2.0/dumb-init_1.2.0_amd64.deb && \
+    dpkg -i dumb-init_1.2.0_amd64.deb && \
+    rm dumb-init_1.2.0_amd64.deb
+
 # explicitly add Gemfile and install dependencies using bundler to make use of
 # Docker's caching
 WORKDIR /osem/
@@ -25,12 +31,13 @@ RUN bundle install --without test development
 
 # add OSEM files and prepare them for use inside a Docker container
 COPY . /osem/
-RUN chown osem.osem /osem/ -R && \
+RUN chown -R osem.root /osem/ && \
+    chmod -R g=u /osem/ && \
     mv /osem/config/database.yml.docker /osem/config/database.yml
 
 # data directory is used to cache the secret key in a file
 ENV DATA_DIR /data
-RUN install -d -m 0700 -o osem $DATA_DIR
+RUN install -d -m 0770 -o osem -g root $DATA_DIR
 VOLUME ["$DATA_DIR"]
 
 USER osem
@@ -42,4 +49,7 @@ COPY docker/init.sh /init.sh
 # from a webserver
 ENV RAILS_SERVE_STATIC_FILES 1
 
+# Runs "/usr/bin/dumb-init -- /my/script --with --args"
+ENTRYPOINT ["/usr/bin/dumb-init", "--"]
+
 CMD ["bash", "/init.sh"]