Switch from using cgroups BlkioThrottleReadIOpsDevice to BlkioWeight

[cbednarski]

Fixes #220

[dadgar]

This is not quite right. We were doing blkio wrong: https://www.kernel.org/doc/Documentation/cgroups/blkio-controller.txt

It has to be device_major:device_minor:limit.

Alternatively we can use BlkioWeight. I think this is the better route to take as it applies across devices.

[dadgar]

BlkioThrottleReadIOpsDevice lets you specify an IOPs limit per device in a cgroup while BlkioWeight applies to all devices and is not a raw IOPs value but rather a weight similar to how cgroups handles CPU. This means under low contention process will have more access to disk and under contention they will be limited correctly.

We are switching to this because it is a more desirable behavior and we don't need to set up cgroups per disk device.

[github-actions]

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