Passing HttpServer port number over the bridge

We have default value 8080 for HttpServer port number . However, when it gets conflict with others, we randomly generate one and assign it on the fly. In order for clients to get it at run time, we would need to pass it over the bridge when setting up the bridge in start handler. 

This PR is to address this issue. https://issues.apache.org/jira/i#browse/REEF-57