Basic perf test for E2E blackbox latency for pod create, get, and list operations

[vinaykul]

What type of PR is this?

Uncomment only one /kind <> line, hit enter to put that in a new line, and remove leading whitespaces from that line:

/kind api-change
/kind bug
/kind cleanup
/kind design
/kind documentation
/kind failing-test
/kind feature
/kind flake

What this PR does / why we need it: Add a basic perf test to e2e framework that can be used to measure blackbox E2E latency for pod create, list and get operations.

Which issue(s) this PR fixes:

Fixes #562

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

Example usage against kubemark cluster:
export KUBECONFIG=/root/go/src/k8s.io/kubernetes/test/kubemark/resources/kubeconfig.kubemark && KUBE_MASTER_IP=<IP of kubemark master> kubetest --test --provider=local --test_args="--ginkgo.focus=PodPerf"