Add an e2e test to assert that autoscaler sustains the required pods … (#4274)
Add an e2e test to assert that autoscaler sustains the required pods … (#4274)

* Add an e2e test to assert that autoscaler sustains the required pods after panicking

* Correct a merging problem

* Add 100ms sleep and generate traffic 2 seconds longer than test duration to improve measurement accuracy.

* Relax the lower bound check a little to reduce flakiness.

* Add documentation and remove 2s extra.

knative/serving,knative/serving