If the IndexerMaster goes down during a batch build then the future containing the callback that updates the batchindex state also disappears. This leaves the indexer in state that it is unable to start new batch jobs.
This change removes the future mechanism and uses a polling mechanism instead.
Add test for multiple indexers.
Make sure we don't get wild growth of checks
A bit of javadoc
Whitespace cleanup
Use a new executor on every test just to be sure