Baremetal host data is still sometimes required

This is a clone of issue OCPBUGS-4874. The following is the description of the original issue:
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OCPBUGS-3278 is supposed to fix the issue where the user was required to provide data about the baremetal hosts (including MAC addresses) in the install-config, even though this data is ignored.

However, we determine whether we should disable the validation by checking the second CLI arg to see if it is agent.

This works when the command is:

openshift-install agent create image --dir=whatever

But fails when the argument is e.g., as in dev-scripts:

openshift-install --log-level=debug --dir=whatever agent create image