public boolean oneOf(String states) {
        for (char c : states.toCharArray()) {
            String s = "" + c;
            if (s.equals(serializedAs)) return true;
        }
        return false;
    }
Defines legal states for various uses. Split this into its own class such
that we can easily see what states are legal to use in what situations.
They double as disk states and node states nodes report they are in, and
wanted states set external sources.
vdslib/src/main/java/com/yahoo/vdslib/state/State.java