Data Source: aws_ami_ids, add sort_ascending flag

[sargun]

This adds the sort ascending flag by creation time to
aws_ami_ids, to allow for a list which only ever adds
items at the end.

This is useful for example, when you have something like this:

data "aws_ami_ids" "agent_amis" {
  owners = ["self"]

  filter {
    name   = "name"
    values = ["foo-*"]
  }
}

data "aws_region" "current" {}

resource "aws_ami_launch_permission" "launch_permissions_1234" {
  count      = "${length(data.aws_ami_ids.agent_amis.ids)}"
  image_id   = "${data.aws_ami_ids.agent_amis.ids[count.index]}"
  account_id = "1234"
}

Otherwise, every time a new AMI is added that matches "foo-*",
it must "recreate" the launch permissions. Although this may
be trivial for launch permissions, on something like AMI
copy, it can wreak havoc.

Changes proposed in this pull request:

• Add sort_ascending flag to data source ami_ids to optionally sort ascending. It will not

Output from acceptance testing:

$ make testacc TESTARGS="-run=TestAccDataSourceAwsAmiIds_sorted"
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test ./... -v -run=TestAccDataSourceAwsAmiIds_sorted -timeout 120m
?   	github.com/terraform-providers/terraform-provider-aws	[no test files]
=== RUN   TestAccDataSourceAwsAmiIds_sorted
--- PASS: TestAccDataSourceAwsAmiIds_sorted (9.65s)
PASS

[sargun]

Since adding a reverse function to Terraform is in purgatory (hashicorp/terraform#18887), I figured might as well add the capability natively here.

[sargun]

This is the same kind of issue that's presented in #155, but because AMIs can be "captured" in time, it avoids this problem, as long as you never delete an AMI.

[sargun]

Also, let me know if you want me to change the acceptance test back, or split that into a separate PR. Waiting for a VM to spin up, and for snapshotting is a pain for waiting for the test to pass, and AFAIK, Amazon Linux is a pretty reliable AMI, as in it hasn't been deleted since 2011.

[bflad]

LGTM, thanks @sargun! 🚀

AWS Commercial:

3 tests passed (all tests)
--- PASS: TestAccDataSourceAwsAmiIds_basic (5.75s)
--- PASS: TestAccDataSourceAwsAmiIds_sorted (10.89s)
--- PASS: TestAccDataSourceAwsAmiIds_empty (14.25s)

AWS GovCloud (US):

3 tests passed (all tests)
--- PASS: TestAccDataSourceAwsAmiIds_basic (1.22s)
--- PASS: TestAccDataSourceAwsAmiIds_sorted (2.37s)
--- PASS: TestAccDataSourceAwsAmiIds_empty (3.03s)

[bflad]

This has been released in version 1.37.0 of the AWS provider. Please see the Terraform documentation on provider versioning or reach out if you need any assistance upgrading.

[ghost]

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If you feel this issue should be reopened, we encourage creating a new issue linking back to this one for added context. Thanks!