add a hot_standby mode, now the default when running HA (although it doesn't do anything, it is a coherent state and the MasterChooser prefers it)
RebindManager is can run in persistence mode or in read-only mode
set up a new ManagementContext.getServerExecutionContext() and use that for node-level tasks, with a tag that can be tracked; improve lifecycle and configuration for rebind exception handler and for the persister itself
improve support for interrupting scheduled tasks and a "wait for interrupted tasks to really complete" method on Tasks; see discussion there, and test case in ScheduledExecutionTest.java
hot standby / read-only rebind is working.  more to do, but this is the guts of it.
use `BrooklynFeatureEnablement` to set whether standby or hot-standby should be the default.
failure going to hot_standby sets not to failure state, not standby state.
rename `EntityReadOnlyInternal` to `EntityTransientCopyInternal`, and remove setDisplayName, as per code review.
better tests (working) for propagating initial items, and test (failing) for update/removal of items being rebinded.
Ensure BrooklynObject management, remanagement, and unmanagement, by replacing Location instances, refreshing the catalog, and swapping out the delegate but keeping the entity proxy.
Better memory leak testing, fixing some leaks, including escaped proxy/reference chains,
and an issue with subscriptions not being cleared when children are removed
(which it turned out was there previously).
support programmatic API on HighAvailabilityManager to changeMode and setPriority;
priority persisted and used to elect master (also prefers non-snapshot and more recent Brooklyn versions by default, unless explicit priority overrides).
good test for changing mode in HotStandbyTest.testChangeMode.
address @sjcorbett review comments
Wait for the actual result of the shutdown call.

Wait indefinitely for the shutdown result, otherwise we get "invalid" success, not aware if there was indeed a shutdown.
address the rest of @sjcorbett's comments
This closes #197
This closes #205