Name for registration code variable is misleading

[r0ckarong]

In the files ci/infra/vmware/registration.auto.tfvars and ci/infra/openstack/registration.auto.tfvars we have a variable called caasp_registry_code this has nothing to do with package registry it's the "registration" code from SCC.

This should be renamed to caasp_registration_code because it's using the wrong term and will confuse users.

Also concerns these files:
ci/infra/openstack/cloud-init/registration.tpl
ci/infra/vmware/cloud-init/registration.tpl