Docker: various updates

- use exec in entrypoint.sh, get rid of extra shell process
- use CMD instead of ENTRYPOINT, so image can be run with /bin/sh arg

docker/Dockerfile

@@ -1,14 +1,16 @@
 FROM alpine:3.6
 
-RUN apk add --no-cache --update apache2-utils
-COPY docker/*_user rest-server /usr/bin/
-COPY docker/entry.sh /
+ENV DATA_DIRECTORY /data
+ENV PASSWORD_FILE /data/.htpasswd
 
-ENV DATA_DIRECTORY=/data
-ENV PASSWORD_FILE=/data/.htpasswd
+RUN apk add --no-cache --update apache2-utils
+
+COPY rest-server docker/*_user /usr/bin/
 
 VOLUME /data
 
 EXPOSE  80
 
-ENTRYPOINT ["/entry.sh"]
+COPY docker/entrypoint.sh /entrypoint.sh
+
+CMD [ "/entrypoint.sh" ]