Description of problem:
When import image from RedHat registry should import the image signature at the same time when setup the configuration about the related registry

Version-Release number of selected component (if applicable):
openshift v3.7.0-0.176.0
kubernetes v1.7.6+a08f5eeb62
etcd 3.2.8

How reproducible:
always

Steps to Reproduce:
1. Build env by jenkins job;
2. Login OpenShift and create project;
3. Setup configuration about the related image registry on all the master:
cat /etc/containers/registries.d/redhat.yaml
docker:
    registry.access.redhat.com:
        sigstore: https://access.redhat.com/webassets/docker/content/sigstore
4. Restart master service: atomic-openshift-master-api,atomic-openshift-master-controllers;
5. As normal user import image from RH registry:
  `oc tag --source=docker registry.access.redhat.com/rhel7 rhel:7`
6. Check the logs from master service: atomic-openshift-master-controllers.

Actual results:
6. No signature imported:
Oct 24 05:39:55 ip-172-18-11-57.ec2.internal atomic-openshift-master-controllers[14147]: I1024 09:39:55.140959   14158 signature_import_controller.go:61] Adding image sha256:a744ef5b58472bccfa7c606efcc6b126a164eee4b7057f85cb8be46c481ee954
Oct 24 05:39:55 ip-172-18-11-57.ec2.internal atomic-openshift-master-controllers[14147]: I1024 09:39:55.140989   14158 signature_import_controller.go:132] Initiating download of signatures for sha256:a744ef5b58472bccfa7c606efcc6b126a164eee4b7057f85cb8be46c481ee954
Oct 24 05:39:55 ip-172-18-11-57.ec2.internal atomic-openshift-master-controllers[14147]: I1024 09:39:55.433944   14158 signature_import_controller.go:148] No signatures dowloaded for sha256:a744ef5b58472bccfa7c606efcc6b126a164eee4b7057f85cb8be46c481ee954



Expected results:
6. The image has signature, should import the signature succeed.


Additional info:
When the OpenShift start by `oc cluster up` could import the image signature succeed.