clarify CPUCFSQuotaPeriod values, set the minimum to 1ms
clarify CPUCFSQuotaPeriod values, set the minimum to 1ms

cpu.cfs_period_us is measured in microseconds in the kernel but
provided in time.Duration by the user, that change clarifies the code
to make this evident to the reader.

Also, the minimum value for that feature is 1ms and not 1μs, and this
change alters the validation to reject values smaller than 1ms.

Kubernetes-commit: d0f9e6dc36fb0f6cfff95988e27eb3796c4e6bce

kubernetes/kubelet