provider/aws: allow destroy of LB stickiness policy with missing LB (#11462)

Previously an attempt to destroy a LB stickiness policy would
result in an error like this:

```
* aws_lb_cookie_stickiness_policy.foo: Error removing LBCookieStickinessPolicy: LoadBalancerNotFound: There is no ACTIVE Load Balancer named 'tf-test-lb-tqatd'
    status code: 400, request id: 28af1167-e4a4-11e6-8ddd-57ba410cbbb6
```

This checks for a missing load balancer on the policy read and allows
the destroy.

```
$ make testacc TEST=./builtin/providers/aws TESTARGS='-run=TestAccAWSLBCookieStickinessPolicy_missingLB'
==> Checking that code complies with gofmt requirements...
go generate $(go list ./... | grep -v /terraform/vendor/)
2017/01/27 07:21:11 Generated command/internal_plugin_list.go
TF_ACC=1 go test ./builtin/providers/aws -v -run=TestAccAWSLBCookieStickinessPolicy_missingLB -timeout 120m
=== RUN   TestAccAWSLBCookieStickinessPolicy_missingLB
--- PASS: TestAccAWSLBCookieStickinessPolicy_missingLB (28.90s)
PASS
ok      github.com/hashicorp/terraform/builtin/providers/aws    28.929s
```

builtin/providers/aws/resource_aws_lb_cookie_stickiness_policy.go

@@ -103,9 +103,10 @@ func resourceAwsLBCookieStickinessPolicyRead(d *schema.ResourceData, meta interf
 
 	getResp, err := elbconn.DescribeLoadBalancerPolicies(request)
 	if err != nil {
-		if ec2err, ok := err.(awserr.Error); ok && ec2err.Code() == "PolicyNotFound" {
-			// The policy is gone.
-			d.SetId("")
+		if ec2err, ok := err.(awserr.Error); ok {
+			if ec2err.Code() == "PolicyNotFound" || ec2err.Code() == "LoadBalancerNotFound" {
+				d.SetId("")
+			}
 			return nil
 		}
 		return fmt.Errorf("Error retrieving policy: %s", err)

builtin/providers/aws/resource_aws_lb_cookie_stickiness_policy_test.go

@@ -149,6 +149,42 @@ func TestAccCheckLBCookieStickinessPolicy_drift(t *testing.T) {
 	})
 }
 
+func TestAccAWSLBCookieStickinessPolicy_missingLB(t *testing.T) {
+	lbName := fmt.Sprintf("tf-test-lb-%s", acctest.RandString(5))
+
+	// check that we can destroy the policy if the LB is missing
+	removeLB := func() {
+		conn := testAccProvider.Meta().(*AWSClient).elbconn
+		deleteElbOpts := elb.DeleteLoadBalancerInput{
+			LoadBalancerName: aws.String(lbName),
+		}
+		if _, err := conn.DeleteLoadBalancer(&deleteElbOpts); err != nil {
+			t.Fatalf("Error deleting ELB: %s", err)
+		}
+	}
+
+	resource.Test(t, resource.TestCase{
+		PreCheck:     func() { testAccPreCheck(t) },
+		Providers:    testAccProviders,
+		CheckDestroy: testAccCheckLBCookieStickinessPolicyDestroy,
+		Steps: []resource.TestStep{
+			resource.TestStep{
+				Config: testAccLBCookieStickinessPolicyConfig(lbName),
+				Check: resource.ComposeTestCheckFunc(
+					testAccCheckLBCookieStickinessPolicy(
+						"aws_elb.lb",
+						"aws_lb_cookie_stickiness_policy.foo",
+					),
+				),
+			},
+			resource.TestStep{
+				PreConfig: removeLB,
+				Config:    testAccLBCookieStickinessPolicyConfigDestroy(lbName),
+			},
+		},
+	})
+}
+
 func testAccLBCookieStickinessPolicyConfig(rName string) string {
 	return fmt.Sprintf(`
 resource "aws_elb" "lb" {
@@ -190,3 +226,18 @@ resource "aws_lb_cookie_stickiness_policy" "foo" {
 	cookie_expiration_period = 300
 }`, rName)
 }
+
+// attempt to destroy the policy, but we'll delete the LB in the PreConfig
+func testAccLBCookieStickinessPolicyConfigDestroy(rName string) string {
+	return fmt.Sprintf(`
+resource "aws_elb" "lb" {
+	name = "%s"
+	availability_zones = ["us-west-2a"]
+	listener {
+		instance_port = 8000
+		instance_protocol = "http"
+		lb_port = 80
+		lb_protocol = "http"
+	}
+}`, rName)
+}