AWS AMI resources

[apparentlymart]

Three new resources for the AWS provider to support the three different methods of creating an AMI:

• aws_ami, using RegisterImage to directly set the various AMI attributes.
• aws_ami_copy, using CopyImage to duplicate an AMI that is possibly in another region
• aws_ami_from_instance, using CreateImage to produce an AMI fashioned after an active or stopped EC2 instance that uses an EBS filesystem

Other tasks:

• Acceptance Tests
• Documentation

[apparentlymart]

This now has acceptance tests for the aws_ami_copy and aws_ami_from_instance resources. Exercising aws_ami itself requires the existence of an EBS snapshot and there isn't yet a resource for creating those, so all we have for now is a FIXME comment noting that we should come back and write an acceptance test once an aws_ebs_snapshot resource is implemented.

aws_ami_copy is the one with the most obvious use-case here: taking an AMI in one region and copying it to another.

aws_ami_from_instance is obviously dependent on having an instance in a good state for a snapshot, which is a hard thing for Terraform alone to arrange. It found utility in my prototype described in #2789, though.

aws_ami will find its most obvious purpose once an aws_ebs_snapshot_copy resource is available, as a way to fake copying AMIs from one account to another by copying the snapshots and creating a fresh AMI from them.

[phinze]

This looks really great, @apparentlymart!

The 3-resources-with-shared-impl model you chose ends up working out very nicely I think. The fact that you only have to implement different Create methods for each resource makes a lot of sense given the relationship between the three.

Totally understandable that we can't AccTest aws_ami yet. I think this looks good to pull in as-is. Amazing work as usual! 😀

[ghost]

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