Fixes ordering in StandaloneUpgrader

[Claudenw]

Fixed issue where sstables were not updated in order by sorting on SSTableId

patch by Claude Warren; reviewed by for CASSANDRA-18143

[jacek-lewandowski]

I suppose it should be a generic method somewhere in the utility class. Something which take a function, for example <T> T generateUntilUnordered(Collection<T> collection, Function<T, T> generator) where generator accepts previously generated value, and initially null.

[Claudenw]

I don't think this will work here. The issue is that the HashSet wraps the values of the hash long before Hash collides. The method literally has to insert into the Hash table and then verify that the last item in the Hash table was the one inserted. I have simplified the code so that it only retains two Descriptors at a time.

[jacek-lewandowski]

I was thinking about something like this:

    static <T> T findFirstUnordered(java.util.function.Function<T, T> provider)
    {
        HashSet<T> set = new HashSet<>(2);
        T first = null;
        while (true)
        {
            set.clear();
            T second = provider.apply(first);
            if (first != null)
            {
                set.add(first);
                set.add(second);
                if (set.iterator().next() != first)
                    return second;
            }
            first = second;
        }
    }