Automatic merge from submit-queue

make certs used in roundtripper_test same as those used in proxy_test

This fixes an invalid cert error in 1.8. Gross copy paste but we will likely never have to do this again.

Part of https://github.com/kubernetes/kubernetes/issues/38228

https://github.com/kubernetes/kubernetes/blame/master/staging/src/k8s.io/apiserver/pkg/endpoints/proxy_test.go#L524-L570