KillEnvoy

This is a reproducer for CVE-2019-15225 (see the underlying issue #7728).

Steps to reproduce:

• deploy an Istio control plane and a httpbin service (see httpbin.yaml in this repo)
• build the binary: go build killenvoy.go
• copy the binary to the httpbin container: kubectl cp kill <NS>/<POD>:/tmp/killenvoy -c httpbin
• run it: kubectl exec -it -n <NS> <POD> -c httpbin -- /tmp/killenvoy
• watch envoy segfault