Fix the knob to enable/disable TSD compactions.
Fix the knob to enable/disable TSD compactions.

Compactions are enabled if the system property
`tsd.feature.compactions' is set and its value
is not the string "false".

Previously the code would enable compactions
as long as the system property was set, which
makes it hard to disable them in the future
once they're enabled by default.

Change-Id: If58a3c269c1b6340c0176fbc793eb9d3fb3dea8e

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