Description:
Envoy does not complete startup if there is a STRICT_DNS cluster with an empty hosts array. It never gets as far as opening listeners.

Repro steps:
Start envoy configured to load the following cluster via CDS:

  - "@type": type.googleapis.com/envoy.api.v2.Cluster
    name: "the_cluster"
    connect_timeout: 2s
    lb_policy: RANDOM
    type: STRICT_DNS
    hosts:  []