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.
Again this logic is surprising given the method name.
Also, the parameter name `newMaster` doesn't feel right, given we're either setting it to be master or standby.