Minor improvement in the code checking cache staleness.
Minor improvement in the code checking cache staleness.

This removes one indirect syscall to `stat'.

Change-Id: If0fa32c698c6dbf51a0ea57f8c3177bde84cc1a4

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