HA uses shared timestamp (last modified time), and negotiates concurrent starts, and handles former master recovery

resubmit of https://github.com/brooklyncentral/brooklyn/pull/1487, adding related code review comments from https://github.com/brooklyncentral/brooklyn/pull/1464, and solving multi-master situations
i want the frequent log messages, to see that sometimes it gets 2 or 3 M nodes then settles down at 1