Use SecurityContextConstraints resource to identify OCP environment

[osmman]

Fixes SECURESIGN-1002

[Gregory-Pereira]

/lgtm

[osmman]

/cherrypick release-1.0

[openshift-cherrypick-robot]

@osmman: once the present PR merges, I will cherry-pick it on top of release-1.0 in a new PR and assign it to you.

In response to this:

/cherrypick release-1.0

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[lance]

/lgtm

I love how I learn new Go packages by just reviewing code. sync.Once is neat.

[openshift-ci]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Gregory-Pereira, lance, osmman

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[openshift-cherrypick-robot]

@osmman: new pull request created: #410

In response to this:

/cherrypick release-1.0

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.