[BUG] Always route to local instance of a service from istio-ingressgateway

[aattuluri]

Describe the bug
When a service name is accessed in a cluster, it's possible for it to bounce between clusters.

Steps To Reproduce
Deploy Service 1 to Cluster 1 and Cluster 2
Deploy Service 2 to Cluster 2
Make a call from Service 2 to Service 1 using global name created by admiral
Notice that some of the calls made from Service 2 to Service 1 take very long time. This is because at the istio-ingressgateway they might be routed back to the original cluster where the request is originating from as that's also a possible destination for that service.

Expected behavior
Service calls using global names should not bounce between clusters.

Proposed solution:
Create a virtual service that always routes calls to the local instance of a service and attach it to istio-ingressgateway gateway
Example:

apiVersion: networking.istio.io/v1alpha3
kind: VirtualService
metadata:
  name: default.greeting.global-default-vs
  namespace: admiral-sync
spec:
  exportTo:
  - '*'
  gateways:
  - istio-multicluster-ingressgateway
  hosts:
  - default.greeting.global
  http:
  - route:
    - destination:
        host: greeting.sample.svc.cluster.local
        port:
          number: 8080