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.
Fix drive rotational calculation status
If a MinIO drive path is mounted to a partition and not a real disk,
getting the rotational status would fail because Linux does not expose
that status to partition; In other words,
/sys/block/drive-partition-name/queue/rotational does not exist;
To fix the issue, the code will search for the rotational status of the
disk that hosts the partition, and this can be calculated from the
real path of /sys/class/block/<drive-partition-name>
slower drives get knocked off because they are too slow via
active monitoring, we do not need to block calls arbitrarily.
Serializing adds latencies for already slow calls, remove
it for SSDs/NVMEs
Also, add a selection with context when writing to `out <-`
channel, to avoid any potential blocks.
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`
