provider/aws: aws_autoscaling_policy fails when setting scaling_adjustment to 0 for SimpleScaling

[denniswebb]

Terraform 0.7.3 incorrectly handles setting scaling_adjustment=0 when using policy_type = "SimpleScaling" although this is allowed in the AWS CLI and Console for all 3 adjustment_types.

The following terraform configuration:

resource "aws_autoscaling_policy" "ok" {
    name = "terraform-test-ok"
    scaling_adjustment = 0
    adjustment_type = "ExactCapacity"
    cooldown = 300
    autoscaling_group_name = "${aws_autoscaling_group.main.name}"
}

will return the error:

* aws_autoscaling_policy.foobar_simple: Error putting scaling policy: ValidationError: Scaling increment must be specified for a SimpleScaling policy
            status code: 400, request id: 0a983458-7c7a-11e6-b90d-c986fdc05768

This is due to the current provider using the GetOk function which doesn't set the value if equal to 0. This PR changes this behavior by using the Get function when the policy_type="SimpleScaling", and falls back to using GetOk when the policy_type isn't.

Below are the acceptance test results.

make testacc TEST=./builtin/providers/aws TESTARGS='-run=AccAWSAutoscalingPolicy_SimpleScalingStepAdjustment'
==> Checking that code complies with gofmt requirements...
go generate $(go list ./... | grep -v /terraform/vendor/)
2016/09/16 21:18:59 Generated command/internal_plugin_list.go
TF_ACC=1 go test ./builtin/providers/aws -v -run=AccAWSAutoscalingPolicy_SimpleScalingStepAdjustment -timeout 120m
=== RUN   TestAccAWSAutoscalingPolicy_SimpleScalingStepAdjustment
--- PASS: TestAccAWSAutoscalingPolicy_SimpleScalingStepAdjustment (43.07s)
PASS
ok      github.com/dennis-bsi/terraform/builtin/providers/aws   43.098s

[denniswebb]

Just realized this should fix #6276

[denniswebb]

@catsby If you're in the merging mood, I have this one that has gotten overlooked that I need in 0.7.8 hopefully.

[catsby]

Thank you @dennis-bsi – this looks good

TF_ACC=1 go test ./builtin/providers/aws -v -run=TestAccAWSAutoscalingPolicy_SimpleScalingStepAdjustment -timeout 120m
=== RUN   TestAccAWSAutoscalingPolicy_SimpleScalingStepAdjustment
--- PASS: TestAccAWSAutoscalingPolicy_SimpleScalingStepAdjustment (38.37s)
PASS
ok      github.com/hashicorp/terraform/builtin/providers/aws    38.386s
Test:

[ghost]

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