code: public boolean isWebSubsystem() throws Exception {
          Address addr = Address.root().add(SUBSYSTEM, SUBSYSTEM_WEB);
          return null != readResource(addr);
      }
docs: Checks to see if the web subsystem exists. This should always exist unless
  the server is just starting up and its web subsystem has not even initialized yet.
  
  @return true if the web subsystem is ready
  @throws Exception any error