CDAP-663 Implemented healthcheck for router and auth-server.

The PR enables health check for router and auth servers independent of downstream services.  
port is selected randomly while setting up the test case. It is not fixed. server.getSocketAddress().toString() does return   IP along with the port number (in the format for e.g. "/127.0.0.1:12345"). I kept hostname and port separate for the readability. Thoughts?