static List<String> getPartiallySealedReplicas(InstanceConfig instanceConfig) {
    return getPartiallySealedReplicas(instanceConfig.getRecord());
  }
Get the list of partially sealed replicas on a given instance.
This is guaranteed to return a non-null list. It would return an empty list if there are no sealed replicas or if
the field itself is absent for this instance.
@param instanceConfig the {@link InstanceConfig} associated with the interested instance.
@return the list of partially sealed replicas.
ambry-clustermap/src/main/java/com/github/ambry/clustermap/ClusterMapUtils.java