Ubuntu element enable clout-init Ec2 Datasource

[Alexis Camilleri]

Hi,

In the code (https://github.com/openstack/diskimage-builder/blob/master/diskimage_builder/elements/ubuntu/environ...), the ubuntu element fallback the cloud-init configuration to an Ec2 datasource when the DIB_CLOUD_INIT_DATASOURCES env var is not set.

I think, it causes confusion.

Context:
I'm building a ubuntu image with theses options "ubuntu custom-cloud-init install-static" and I would configured a cloud-init NoCloud datasource and hardcode the seedfrom path to a local metadata api url, this is done by my custom-cloud-init element.