Automatic merge from submit-queue
[garbage collector] add e2e test
This PR also includes some changes to plumb controller-manager's `--enable_garbage_collector` from the environment variable.
The e2e test will not be run by the core suite because it's marked `[Feature:GarbageCollector]`.
The corresponding jenkins job configuration PR is https://github.com/kubernetes/test-infra/pull/132.
01e34b72c1