Revert "Include every IP address into a cert's SAN field"

[ananace]

Reverts #32

To copy what I said there;
It's causing issues as it's changing the SAN list - and therefore also triggering a recreation of the serving certs - every time a container starts or stops on the Kubernetes master nodes.

Additionally, it's also including link-local bindings as well as IPVS entries from kube-proxy into the certificates, which causes the SAN list to grow in size far too quickly. A simple test cluster with no active load is already up to 50 SANs, while our production cluster would have SAN lists with almost a thousand entries for each master.

[ananace]

I've also added an $addn_names parameter to k8s::server::etcd, so that additional IP addresses can be specified for the non-default address use-case. It's slightly less optimal than automatically generating the list, but at least it won't cause issues for the common use-case.