Brooklyn node and cluster upgrade

Merges #266 (cluster upgrade) with work I've been doing on node upgrade.

Builds on #260 so please ensure that is merged first.

Needs further testing (by me at this point) but wanted to push it in case @neykov you have comments, especially on the last commit.
`Sets.newLinkedHashSet(initialMembers)`. I much prefer the determinism of a LinkedHashSet. But probably not important here as we'll execute stop in parallel on them all.