https://issues.redhat.com//browse/OCPBUGS-31919 partially fixed an issue consuming the test image from a custom registry.
The fix is about consuming in the test binary the pull-secret of the cluster under tests.
To complete it we have to do the same trusting custom CA as the cluster under test.

Without that, if the test image is exposed by a registry where the TLS cert is signed by a custom CA, the same tests will fail as for:

{  fail [github.com/openshift/origin/test/extended/operators/certs.go:120]: Unexpected error:
    <*errors.errorString | 0xc0023105c0>: 
    unable to determine openshift-tests image oc wrapper with cluster ps: Error running /usr/bin/oc adm release info virthost.ostest.test.metalkube.org:5000/localimages/local-release-image@sha256:d368cc92e8d274744aac655e070d3a346f351fc5bd5f18a227b73452fd5c58b7 --image-for=tests --registry-config /tmp/image-pull-secret2435751342:
    StdOut>
    error: unable to read image virthost.ostest.test.metalkube.org:5000/localimages/local-release-image@sha256:d368cc92e8d274744aac655e070d3a346f351fc5bd5f18a227b73452fd5c58b7: Get "https://virthost.ostest.test.metalkube.org:5000/v2/": tls: failed to verify certificate: x509: certificate signed by unknown authority
    StdErr>
    error: unable to read image virthost.ostest.test.metalkube.org:5000/localimages/local-release-image@sha256:d368cc92e8d274744aac655e070d3a346f351fc5bd5f18a227b73452fd5c58b7: Get "https://virthost.ostest.test.metalkube.org:5000/v2/": tls: failed to verify certificate: x509: certificate signed by unknown authority
    exit status 1
    
    {
        s: "unable to determine openshift-tests image oc wrapper with cluster ps: Error running /usr/bin/oc adm release info virthost.ostest.test.metalkube.org:5000/localimages/local-release-image@sha256:d368cc92e8d274744aac655e070d3a346f351fc5bd5f18a227b73452fd5c58b7 --image-for=tests --registry-config /tmp/image-pull-secret2435751342:\nStdOut>\nerror: unable to read image virthost.ostest.test.metalkube.org:5000/localimages/local-release-image@sha256:d368cc92e8d274744aac655e070d3a346f351fc5bd5f18a227b73452fd5c58b7: Get \"https://virthost.ostest.test.metalkube.org:5000/v2/\": tls: failed to verify certificate: x509: certificate signed by unknown authority\nStdErr>\nerror: unable to read image virthost.ostest.test.metalkube.org:5000/localimages/local-release-image@sha256:d368cc92e8d274744aac655e070d3a346f351fc5bd5f18a227b73452fd5c58b7: Get \"https://virthost.ostest.test.metalkube.org:5000/v2/\": tls: failed to verify certificate: x509: certificate signed by unknown authority\nexit status 1\n",
    }
occurred
Ginkgo exit error 1: exit with code 1}

    release-4.16, release-4.17 and master branchs in origin.

Always    

    1. try to run the test suite against a cluster where the OCP release (and the test image) comes from a private registry with a cert signed by a custom CA
    2.
    3.
    

    3 failing tests:
: [sig-arch][Late][Jira:"kube-apiserver"] collect certificate data [Suite:openshift/conformance/parallel] expand_more
: [sig-arch][Late][Jira:"kube-apiserver"] all registered tls artifacts must have no metadata violation regressions [Suite:openshift/conformance/parallel] expand_more
: [sig-arch][Late][Jira:"kube-apiserver"] all tls artifacts must be registered [Suite:openshift/conformance/parallel] expand_more

    No failing tests

    OCPBUGS-31919 partially fixed it having the test binary downloading the pull secret from the cluster under test. But in order to have it working we have also to trust custom CAs trusted by the cluster under test