allow nova boot with scheduler hints like group="groupId"

ServerCreate sc = Builders.server().flavor("1").networks(net).image("1").name("hehe234").build();
Map<String, String> hints = new HashMap<String, String>();
hints.put("group", "46c2b4c9-5b6a-4a45-9097-fbcee3a08f32");
Server server = os.compute().servers().bootWithSchedulerHints(sc, hints);