DRILL-2977, DRILL-2978: Swap fragment execution method implementations, and cancellation changes
Execution: In WorkManager,
+ swap implementations of startFragmentPendingRemote() and addFragmentRunner()
+ warn if there are running fragments in close()
Cancellation:
+ for fragments waiting on data, delegate cancellations to WorkEventBus (in Foreman and ControlMessageHandler)
+ documentation
