Currently, we read from `/proc/diskstats` which is found to be
un-reliable in k8s environments. We can read from `sysfs` instead.
Also, cache the latest drive io stats to find the diff and update
the metrics.
This is to ensure that there are no projects
that try to import `minio/minio/pkg` into
their own repo. Any such common packages should
go to `https://github.com/minio/pkg`
