Change dockerfile for oc-mirror OKD

[jupierce]

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[jupierce]

/cherry-pick openshift-4.18

[openshift-cherrypick-robot]

@jupierce: once the present PR merges, I will cherry-pick it on top of openshift-4.18 in a new PR and assign it to you.

In response to this:

/cherry-pick openshift-4.18

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[openshift-cherrypick-robot]

@jupierce: new pull request created: #5671

In response to this:

/cherry-pick openshift-4.18

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository.