code: public B withConfigPath(String path) {
          assertNotNull(path, "path could not be null.");
          withConfigProperties(EmbedVaadinConfig.loadProperties(path));
          return self();
      }
docs: Loads a configuration file from the specified location. Fails if the
  specified <tt>path</tt> does not exist.
  
  @param path the location of a properties file in the classpath
  @return this
  @throws IllegalStateException if no such properties file is found