- If the Docker storage driver is devicemapper, and the devicemapper device is *not* loopback, fix
an issue where the device associated with the / mount point was being assigned LabelDockerImages,
instead of the devicemapper device
- If the devicemapper device is a loopback device, don't assign it LabelDockerImages; instead,
report the underlying partition's information
Read disk io information from /proc/diskstats.
This will allow the user who provides partition container hints to get partition-specific io (blkio provides io for the container, but at the disk device level).