Purge logstash data older than a configurable number of days; use isvcs:v17

Remove unused function

Run the purge 10 mins after startup, every 6 hours thereafter

Verify we have a container id before running a command
Merge pull request #1039 from control-center/feature/ZEN-14075-purge

Purge logstash data older than a configurable number of days; use isvcs:v17