Don't use statically defined Endpoints in tests

Instead, let K8s create the Endpoints (Endpointslices) per Deployments.

For headless services, this requires adjusting tests to account for dynamically assigned IPs.

This further complicates testing ipv6 and dual stack cases.
For now, just fall back to testing ipv4, and leave ipv6 and dual stack tests to be handled later.

This may be an opportunity to re-implement the integrations tests entirely (e.g. moving away from circle ci) - perhaps moving them into coredns/coredns (which would greatly facilitate coordinating test and function changes).