Handle missing OpenAPI specs on aggregated servers
Handle missing OpenAPI specs on aggregated servers

Previously, the aggregator would fail to actually set up the aggregator
proxy for an API server that was missing an OpenAPI spec.  It would show
up in discovery, but the actual proxying would fail to occur.

Now, we simply log an error if we can't fetch an OpenAPI spec for a
particular aggregated server, and continue on.

Kubernetes-commit: 17eb58131a29c7299299fa8c690bcf8fa4c20c84

caesarxuchao/kube-aggregator,caesarxuchao/kube-aggregator,caesarxuchao/kube-aggregator,kubernetes/kube-aggregator,kubernetes/kube-aggregator