Handle failure to flush the compaction queue when shutting down.
Handle failure to flush the compaction queue when shutting down.

This fixes #111.

Change-Id: I3b1eab3fc1f884d960d4ac9c8fdc46edf1bfdea9

OpenTSDB/opentsdb,alienth/opentsdb,sidhhu/opentsdb,kidaa/opentsdb,andyflury/opentsdb,eswdd/opentsdb,MadDogTechnology/opentsdb,eswdd/opentsdb,MadDogTechnology/opentsdb,OpenTSDB/opentsdb,ShefronYudy/opentsdb,kidaa/opentsdb,OpenTSDB/opentsdb,MadDogTechnology/opentsdb,johann8384/opentsdb,johann8384/opentsdb,alienth/opentsdb,sidhhu/opentsdb,ShefronYudy/opentsdb,andyflury/opentsdb