Low disk space on docker-omnibus.gitlap.com node

On 07:38 UTC there was alert about low disk space on docker-omnibus.gitlap.com.

After cleaning docker images and restarting docker service - used space is 17%.

This alert also doesn't have correctly expanded message because of #1436 (closed).

@rspeicher this is the alert with the empty title, which you noticed in the alerts channel.

closing it, since it is resolved for now.

/cc @pcarranza @rspeicher @marin