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.
We should put this in the try-block as well, to guarantee that we unset `upgradeInProgress`, even if there `checkNotNull` below fails.