WIP gearD - Remove failed containers from runtime

* "Failed" is determined as non-zero exit code and a gearD managed container
WIP gearD - test for cleanup_failure.go
WIP gearD - Refactor from reviews

* Added retentionAge
* Removed DryRun special messaging
* Removed container prefix check
* Updated tests
WIP gearD - Refactor from reviews

* Skip containers with name ending in '-data'
WIP gearD - test for cleanup_failure.go

* Bad error message
Merge pull request #83 from jwhonce/wip/gear_repair

Remove failed containers from runtime