Signal to downstream processes when a run is complete

[kjsanger]

The objective is to avoid downstream processes needing to use heuristics to tell if a run has completed (and completed copying too). The sequencing_summary.txt should be the last file to be created by the run. However, it may not be the last file to arrive at the destination when there are concurrent copy operations in progress. One option is to copy sequencing_summary.txt copy only after a period of idle time. This doesn't guard against the run being restarted (but does that create a new run folder?)