code: @SafeVarargs
      public static void enableBundles(final Class<? extends GuiceyBundle>... bundles) {
          final String prop = Joiner.on(',').join(toStrings(Lists.newArrayList(bundles)));
          System.setProperty(BUNDLES_PROPERTY, prop);
      }
docs: Sets system property value to provided classes. Shortcut is useful to set property from code, for example,
  in unit tests.
  
  @param bundles bundles to enable