The intention of the code was to have one-hop-away workers list KMS
workers to get initial upstreams, and have other workers continue using
what was in their config file. However, nothing stops people from having
initial_upstreams but _also_ adding a cluster ID in their config file,
in which case we'd always run this check and replace the config-set
initial upstreams. So, ensure the config-set initial upstreams is also
len zero.
Jeff Mitchell
07bca9dd66