resource/aws_appautoscaling_target: Prevent state removal at creation (…

…#11819)

References
* #11811

The AWS application-autoscaling service has eventual consistency
considerations. The `aws_appautoscaling_target` resource immediately
tries to read a scaling target after creation. If the target is not
found, the application-autoscaling service returns a 200 OK with an
empty list of scaling targets. Since no scaling target is present, the
`aws_appautoscaling_target` resource removes the created resource from
state, leading to a "produced an unexpected new value for was present,
but now absent" error.

With the changes in this commit, the empty list of scaling targets in
the response for the newly created resource will result in a
NotFoundError being returned and a retry of the read request. A
subsequent retry should hopefully be successful, leading to the state
being preserved.

Output from acceptance testing:

```
> make testacc TEST=./aws TESTARGS='-run=TestAccAWSAppautoScalingTarget_'
...
--- PASS: TestAccAWSAppautoScalingTarget_multipleTargets (30.77s)
--- PASS: TestAccAWSAppautoScalingTarget_optionalRoleArn (32.50s)
--- PASS: TestAccAWSAppautoScalingTarget_spotFleetRequest (77.50s)
--- PASS: TestAccAWSAppautoScalingTarget_basic (107.66s)
--- PASS: TestAccAWSAppautoScalingTarget_emrCluster (783.20s)
```

aws/resource_aws_appautoscaling_target.go

@@ -102,11 +102,28 @@ func resourceAwsAppautoscalingTargetPut(d *schema.ResourceData, meta interface{}
 }
 
 func resourceAwsAppautoscalingTargetRead(d *schema.ResourceData, meta interface{}) error {
+	var t *applicationautoscaling.ScalableTarget
+
 	conn := meta.(*AWSClient).appautoscalingconn
 
 	namespace := d.Get("service_namespace").(string)
 	dimension := d.Get("scalable_dimension").(string)
-	t, err := getAwsAppautoscalingTarget(d.Id(), namespace, dimension, conn)
+
+	err := resource.Retry(2*time.Minute, func() *resource.RetryError {
+		var err error
+		t, err = getAwsAppautoscalingTarget(d.Id(), namespace, dimension, conn)
+		if err != nil {
+			return resource.NonRetryableError(err)
+		}
+		if d.IsNewResource() && t == nil {
+			return resource.RetryableError(&resource.NotFoundError{})
+		}
+		return nil
+	})
+	if isResourceTimeoutError(err) {
+		t, err = getAwsAppautoscalingTarget(d.Id(), namespace, dimension, conn)
+	}
+
 	if err != nil {
 		return err
 	}