./scripts/validate-autoinstall-user-data is used by the integration
tests to verify the written user data validates against the combined
JSON schema, but we have introduced run-time checks for more things
than can be caught by simple JSON validation (e.g. warns/errors on
unknown keys or strict top-level key checking for supporting a
top-level "autoinstall" keyword in the non-cloud-config delivery
scenario). This changes the validation script to rely on the logic
from the server directly to perform pre-validation of the the
supplied autoinstall configuration.
Additionally, this adds an argparser to make it more user-friendly.
Now we can advertise this script as something for users to pre-validate
their autoinstall configurations.