HPCC-8789 - Pausenow could fail to abort and lose spills

The pausenow feature, aborts the current subgraph and preserves
the unconsumed spills of completed subgraphs.
If the abort took too long, thor recycled, before the spills
were saved. Since the job was marked paused and resumable, when
it was resumed, if the spills were missing, it would complain and
fail.

Ensure spills are saved away earlier, abort asynchronously and
only kick off the fatal timeout, once the spills have been saved

Signed-off-by: Jake Smith <jake.smith@lexisnexis.com>