prairiedog: if the variant doesn't support boot settings be okay with…

[jmt-lab]

… None

Description of changes:

• Made the reading method to return None should the file not exist.

Testing done:

• Launched aws-ecs-1 and ensured it properly joined the ecs cluster

Terms of contribution:

By submitting this pull request, I agree that this contribution is dual-licensed under the terms of both the Apache License, version 2.0, and the MIT license.

[webern]

I'm not clear on why we are hitting these cases where a template file isn't rendered yet. I will need help creating a mental model of what is happening during template rendering (i.e. order of ops).

[arnaldo2792]

@webern, the case that I saw was that in aws-ecs-1, the bootconfig.toml defaults aren't used. With the ongoing work to use configuration files instead of API calls, the generation of the configuration for prairiedog was moved to the API. Since the service that creates the configuration file is added by the bootconfig.toml defaults, the file is never rendered for aws-ecs-1.