preload: should delete container / fail gracefully if balena-image-preloader is in use

[kendallgoto]

Expected Behavior

balena preload should always succeed or fail gracefully if necessary

Actual Behavior

If balena preload runs and is interrupted unexpectedly, it leaves a container behind with a static name. Since it doesn't clean itself up, this then prevents balena preload from running again, since that static name is already taken:

(HTTP code 409) unexpected - Conflict. The container name "/balena-image-preloader" is already in use by container "..."

Instead, the service should either gracefully remove balena-image-preloader (if it is not really in use) or fail with a correlating error (i.e. if balena preload is actually running at the same time).

Steps to Reproduce the Problem

1. run balena preload operation
2. kill the balena task abruptly
3. run balena preload again
4. balena preload will fail, the balena-image-preloader will remain running and present until it is manually killed

Specifications

• balena CLI 16.7.5
• balenaCloud
• 64bit linux