Currently, cAdvisor calls into libcontainer to collect container stats. However, cAdvisor doesn't export these stats. With CRI-O adding support for the metrics cAdvisor reports, it would be easiest if there was a library that exported this stats collection.

This serves as a good opportunity to refactor libcontainer's stats API to support more of the use cases cAdvisor and CRi-O need. That will allow deduplication, and a more general stats collection API.