Revist simple preemption example

Previous, if I followed the steps in preemption example, there will have 2 pods running from "normal-priority-job-with-9999-priority" job before the cleanup step.

• https://github.com/apache/yunikorn-k8shim/tree/master/deployments/examples/preemption

But I only got 1 "normal-priority-job-with-9999-priority" pod in 1.6.0-rc2.

Need to conduct comprehensive investigation and confirm whether it's expected.
If it's expected, the document must be fixed.