provider/aws: Always set ipv6 addresses in read

[catsby]

Fixes an issue where ipv6_addresses are not set in EC2 Classic environments.

Fixes several tests like TestAccAWSInstance_keyPairCheck, TestAccAWSInstanceDataSource_keyPair, several others, that are failing because of the ipv6_addresses is detecting drift:

--- FAIL: TestAccAWSInstance_keyPairCheck (180.16s)
    testing.go:265: Step 0 error: After applying this step, the plan was not empty:
        
        DIFF:
        
        DESTROY/CREATE: aws_instance.foo
          availability_zone:           "us-east-1c" => "<computed>"
          ipv6_addresses.#:            "" => "<computed>" (forces new resource)
          key_name:                    "tmp-key" => "tmp-key"

Some tests:

# us-east-1 test
TF_ACC=1 go test ./builtin/providers/aws -v -run=TestAccAWSInstance_keyPairCheck -timeout 120m
=== RUN   TestAccAWSInstance_keyPairCheck.             
--- PASS: TestAccAWSInstance_keyPairCheck (99.93s)
PASS


# us-west-2 test
TF_ACC=1 go test ./builtin/providers/aws -v -run=TestAccAWSInstance_basic -timeout 120m
=== RUN   TestAccAWSInstance_basic
--- PASS: TestAccAWSInstance_basic (134.37s)
PASS
ok  	github.com/hashicorp/terraform/builtin/providers/aws	134.398s

[grubernaut]

LGTM!

[ghost]

I'm going to lock this issue because it has been closed for 30 days ⏳. This helps our maintainers find and focus on the active issues.

If you have found a problem that seems similar to this, please open a new issue and complete the issue template so we can capture all the details necessary to investigate further.