Rebase openshift/CoreDNS to CoreDNS v1.8.1

This story is for actually updating the version of CoreDNS in github.com/openshift/coredns. Our fork will need to be rebased onto https://github.com/coredns/coredns/releases/tag/v1.8.1, which may involve some git fu. Refer to previous CoreDNS Rebase PR's for any pointers there.