Automatic merge from submit-queue
Add density (batch pods creation latency and resource) and resource performance tests to `test-e2e-node'
This PR contains two new tests (migrate from e2e test):
1. Density test: verify startup latency and resource usage when create a batch of pod with throughput control. Throughput control is done by sleep for an interval between firing concurrently create pod operations.
It tests both batch creation and sequential (back-to-back) creation and report the throughputs.
2. Verify resource usage of steady state kubelet.
The test creates a new resource controller for `test-node-e2e' (resource_controller.go) which monitors resource through a standalone Cadvisor pod (port 8090) with 1s housekeeping interval.
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