(GH-962) Allow Amazon Linux 2 and newer versions

[rjd1]

Summary

Modified validation code to permit running on Amazon Linux 2 and newer versions.

Additional Context

See the linked issue.

Related Issues (if any)

https://github.com/puppetlabs/puppetlabs-docker/issues/962

Checklist

• [ ] 🟢 Spec tests.
• [ ] 🟢 Acceptance tests.
• [ x] Manually verified. (For example puppet apply)