[rhol_crc] add_crc_creds: Fix check for kubeconfig

[elfiesmelfie]

The check currently doesn't provide any feedback when the kubeconfig doesn't exist in the expected location.
If the kubeconfig doesn't exist in the expected location, there should be an error. This enhances the user experience by telling them the issue right away.

The error come up here: https://review.rdoproject.org/zuul/build/f77349f5e5cb4fff829e5272f04f5b0b/console#9/0/6/controller

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• Appropriate testing is done and actually running
• Appropriate documentation exists and/or is up-to-date:
  • README in the role
  • Content of the docs/source is reflecting the changes

[openshift-ci]

Hi @elfiesmelfie. Thanks for your PR.

I'm waiting for a openstack-k8s-operators member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[pablintino]

/ok-to-test
/approve

[openshift-ci]

[APPROVALNOTIFIER] This PR is APPROVED

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