provider/aws: fix CheckDestroy for ProtocolPolicy tests

Can only assert that the load balancer is gone, since the test suite
deletes everything, and the load balancer is the way you get to the
proxy protocol policy.

builtin/providers/aws/resource_aws_proxy_protocol_policy_test.go

@@ -4,6 +4,8 @@ import (
 	"fmt"
 	"testing"
 
+	"github.com/aws/aws-sdk-go/aws"
+	"github.com/aws/aws-sdk-go/service/elb"
 	"github.com/hashicorp/terraform/helper/resource"
 	"github.com/hashicorp/terraform/terraform"
 )
@@ -43,10 +45,28 @@ func TestAccAWSProxyProtocolPolicy_basic(t *testing.T) {
 }
 
 func testAccCheckProxyProtocolPolicyDestroy(s *terraform.State) error {
-	if len(s.RootModule().Resources) > 0 {
-		return fmt.Errorf("Expected all resources to be gone, but found: %#v", s.RootModule().Resources)
+	conn := testAccProvider.Meta().(*AWSClient).elbconn
+
+	for _, rs := range s.RootModule().Resources {
+		if rs.Type != "aws_placement_group" {
+			continue
 		}
 
+		req := &elb.DescribeLoadBalancersInput{
+			LoadBalancerNames: []*string{
+				aws.String(rs.Primary.Attributes["load_balancer"])},
+		}
+		_, err := conn.DescribeLoadBalancers(req)
+		if err != nil {
+			// Verify the error is what we want
+			if isLoadBalancerNotFound(err) {
+				continue
+			}
+			return err
+		}
+
+		return fmt.Errorf("still exists")
+	}
 	return nil
 }