Allow relative time specification ("1d-ago") in HTTP queries.
Allow relative time specification ("1d-ago") in HTTP queries.

This makes it easier to build dashboards.

Change-Id: Id07646b7a05f5d75713bf641913a5f6c9aae2e95

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