Issue #2223063: Only call task confirm form when required.
We add an AJAX callback to simply replace the task list when a button
is clicked. Currently, this does not refresh the queue block, nor set
the shorter timeout on polling the queue.
Allow getting the queue status for individual nodes.
We add hosting_task_count_status(), which generalizes the counting of
queued items of a given status, and allows for an optional NID. We then
re-use it in hosting_task_count() and hosting_task_count_running(), thus
allowing us to pass an NID into either of these too.