title: Istio fails with "no healthy upstream" when I have "subset" set on all destinations
body: <p>Below is my VirtualService YAML. If I don't comment the below-marked line (subset: v1) then any request fails with "no healthy upstream".</p>
  
  <p>Any idea, why this could be an issue?</p>
  
  <pre><code>apiVersion: networking.istio.io/v1alpha3
  kind: VirtualService
  metadata:
    name: dragon-vs
    namespace: flight
  spec:
    hosts:
    - "*" 
    gateways:
      - dragon-gateway
    http:
    - match:
      - uri:
          prefix: /api/values
      route:
      - destination:
          host: dragon.flight.svc.cluster.local
          subset: v1 ## !!! this is the problem !!! ## 
        weight: 95
      - destination:
          host: dragon.flight.svc.cluster.local
          subset: v2
        weight: 5
  </code></pre>