Feature: DB host during docker run time from entry.sh script

[mmuller88]

The location of the postgres DB isn't important at the docker build time only at the docker run time. So it makes sense to create a helper script that configures the config to use the DB host given from an Env variable and runs the webserver afterwards and calls it perhaps entry.sh similar to this:

sed -i "s/localhost/${R3_DB_HOST}/g" config_template.json 
/opt/r3/r3 -run -config /opt/r3/data/config.json

The last like of the docker file would look like:

CMD ["entry.sh"]

This way you don't need to rebuild the docker image when the db changed.