How to gracefully stop TSDB

[KMax]

Currently TSDB doesn't flush the observations which are kept in the memory to disk before stop, therefore we lose these observations. So we need to find a way to somehow request TSDB to flush the observations to the disk before the stop.

[garayzuev]

This issue is related with #68 TSDB doesn't start after reboot

[garayzuev]

If you stop hbase by command docker stop -t 60 hbase or another command with waiting while hbase shut down, hbase stopes gracefully and then TSDB stopes the same. And this case provides that hbase and TSDB start good.