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

The PR enables health check for router and auth servers independent of downstream services.  
I don't think we need to start and stop the auth server and LDAP server independently for each and every test.  I would move the auth server and LDAP server start into the setup() method, and the stop into the afterClass() method.

The testStartStopServer() method which does test starting and stopping, I don't think adds much value.  I think we can remove it.