GeezerVison

Summary:
Tiny dev_dns_updater papercut: if a LoadBalancer reports a hostname and local DNS can't resolve it yet, the updater used to ignore the lookup error and index ip[0]. That can panic instead of waiting for the next Service update. This now logs the miss and keeps watching, no drama.

Relevant Issues:
Related #484
Related #2209

Type of change:
/kind bug

Test Plan:
Repro: send watchForExternalIP a Service event with status.loadBalancer.ingress[0].hostname set, while DNS lookup returns an error or no IPs. Before this change it hits ip[0] and panics; after this change it skips that update and keeps running.

go test ./src/utils/dev_dns_updater
bazel test //src/utils/dev_dns_updater:dev_dns_updater_test --test_output=errors

Changelog Message:
N/A

Additional documentation:
N/A