Operator mirroring for disconnected install in OpenShift 4 ignores the operator index image

Issue

• After mirroring a selection of four operators for a disconnected install they consume a lot of disk space.

The operators were mirrored using the following commands to a local mirror registry:

opm index prune \
    -f registry.redhat.io/redhat/redhat-operator-index:v4.8 \
    -p kubernetes-nmstate-operator,local-storage-operator,elasticsearch-operator,cluster-logging \
    -t local-registry:8443/redhat/redhat-operator-index:v4.8

oc adm catalog mirror -a ./pullsecret.json --insecure \
    local-registry:8443/redhat/redhat-operator-index:v4.8 \
    local-registry:8443 \
    --index-filter-by-os='linux/amd64'

info: Mirroring completed in 2h28m41.06s (4.634MB/s)

After the mirroring was complete, the mirror was using over 70GiB of disk space.