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

The PR enables health check for router and auth servers independent of downstream services.  
You can also use `ProgramFlowUtil.waitFor()` to accomplish this: https://github.com/caskdata/cdap/blob/develop/cdap-client/src/main/java/co/cask/cdap/client/util/ProgramFlowUtil.java