Fix Docker builds

Fixes CDAP-1080 (Docker builds and starts CDAP, but HelloWorld doesn't run). 

This creates a property (router.address) that can be set on the Java command line inside a Docker container to the correct IP address, yet at the same time it doesn't interfere with a regular Standalone installation from successfully using localhost (127.0.0.1) as the IP to bind to.

Tested on a Standalone and Docker build.