Description of problem:
When the external repo of image changed, but the digest of image not change, in OpenShift the 'DOCKER REF' of the image still use the old one, then the pullthough function can't work .

Version-Release number of selected component (if applicable):
openshift version
openshift v3.5.0.54
kubernetes v1.5.2+43a9be4
etcd 3.1.0

How reproducible:
always

Steps to Reproduce:
1. Login openshift and create project;
2. Create a private registry in the user's project:
   `oc new-app --docker-image=registry:2`
3. Wait for the private registry running, push image to the private registry:
   `docker login -u user -p password  service_of_private_registry`
   `docker pull docker.io/busybox & docker tag docker.io/busybox service_of_private_registry/project/busybox:latest & docker push service_of_private_registry/project/busybox:latest`
4. Tag image from the private registry to local project:
   `oc tag service_of_private_registry/project/busybox:latest  myimagestream:latest`
5. Try to pull the imagestream, will succeed;
6. Delete the project and all the resource;
7. Create new project and repeat step2~ step5, the new imagestream will pull failed.


Actual results:
4. Check the image object, the 'DOCKER REF' of the image use the service of the private registry:
   `oc get images |grep 7685ee1d1b2b1c97ce73dc75248af94f1232288a0f8abe4edf8b3842b2294169`
sha256:7685ee1d1b2b1c97ce73dc75248af94f1232288a0f8abe4edf8b3842b2294169   172.30.49.41:5000/terga/busybox@sha256:7685ee1d1b2b1c97ce73dc75248af94f1232288a0f8abe4edf8b3842b2294169
7. The new imagestream pull failed with error: manifest unknown: manifest unknown

Expected results:
7. Should use the latest private registry service , and pull the imagestream succeed.

Additional info:
   Check the image object, still use the service of the old private registry, and logs from integrated docker-registry:
[root@host-8-175-119 origin]# oc get images |grep 7685ee1d1b2b1c97ce73dc75248af94f1232288a0f8abe4edf8b3842b2294169
sha256:7685ee1d1b2b1c97ce73dc75248af94f1232288a0f8abe4edf8b3842b2294169     172.30.49.41:5000/terga/busybox@sha256:7685ee1d1b2b1c97ce73dc75248af94f1232288a0f8abe4edf8b3842b2294169

time="2017-03-17T02:53:07.688650433Z"  level=error msg="error getting remote repository for image  \"172.30.49.41:5000/terga/busybox:latest\": Get http://172.30.49.41:5000/v2/:  dial tcp 172.30.49.41:5000: getsockopt: no route to host"  go.version=go1.7.4 http.request.host="172.30.69.20:5000"  http.request.id=817f1519-85c1-4cfd-8704-a1afc949b4cf  http.request.method=GET http.request.remoteaddr="10.128.0.1:37712"  http.request.uri="/v2/wf7d0/mystream/manifests/latest"  http.request.useragent="docker/1.12.6 go/go1.7.4  kernel/3.10.0-514.10.2.el7.x86_64 os/linux arch/amd64  UpstreamClient(Docker-Client/1.12.6 \\(linux\\))"  instance.id=33a1698f-0f3b-45ef-9e28-08f4c6a304bb  openshift.auth.user=anonymous openshift.logger=registry  vars.name="wf7d0/mystream" vars.reference=latest 
time="2017-03-17T02:53:07.688787114Z"  level=error msg="response completed with error" err.code="manifest  unknown" err.detail="Get http://172.30.49.41:5000/v2/:  dial tcp 172.30.49.41:5000: getsockopt: no route to host"  err.message="manifest unknown" go.version=go1.7.4  http.request.host="172.30.69.20:5000"  http.request.id=817f1519-85c1-4cfd-8704-a1afc949b4cf  http.request.method=GET http.request.remoteaddr="10.128.0.1:37712"  http.request.uri="/v2/wf7d0/mystream/manifests/latest"  http.request.useragent="docker/1.12.6 go/go1.7.4  kernel/3.10.0-514.10.2.el7.x86_64 os/linux arch/amd64  UpstreamClient(Docker-Client/1.12.6 \\(linux\\))"  http.response.contenttype="application/json; charset=utf-8"  http.response.duration=7.261142961s http.response.status=404  http.response.written=267  instance.id=33a1698f-0f3b-45ef-9e28-08f4c6a304bb  openshift.auth.user=anonymous openshift.logger=registry  vars.name="wf7d0/mystream" vars.reference=latest 
10.128.0.1  - - [17/Mar/2017:02:53:00 +0000] "GET  /v2/wf7d0/mystream/manifests/latest HTTP/1.1" 404 267 "" "docker/1.12.6  go/go1.7.4 kernel/3.10.0-514.10.2.el7.x86_64 os/linux arch/amd64  UpstreamClient(Docker-Client/1.12.6 \\(linux\\))"