Include more information when multiple security groups are tagged

When trying to create ELB we can sometime fail if there is more then one AWS
security group tagged. It very useful to get the list of security groups printed in
the error message.

**Release note**:

```release-note
  Include the list of security groups when failing with the errors that more then one is tagged
```

pkg/cloudprovider/providers/aws/aws.go

@@ -3653,7 +3653,11 @@ func findSecurityGroupForInstance(instance *ec2.Instance, taggedSecurityGroups m
 		// We create instances with one SG
 		// If users create multiple SGs, they must tag one of them as being k8s owned
 		if len(tagged) != 1 {
-			return nil, fmt.Errorf("Multiple tagged security groups found for instance %s; ensure only the k8s security group is tagged", instanceID)
+			taggedGroups := ""
+			for _, v := range tagged {
+				taggedGroups += fmt.Sprintf("%s(%s) ", *v.GroupId, *v.GroupName)
+			}
+			return nil, fmt.Errorf("Multiple tagged security groups found for instance %s; ensure only the k8s security group is tagged; the tagged groups were %v", instanceID, taggedGroups)
 		}
 		return tagged[0], nil
 	}

pkg/cloudprovider/providers/aws/aws_test.go

@@ -1302,6 +1302,29 @@ func TestEnsureLoadBalancerHealthCheck(t *testing.T) {
 	})
 }
 
+func TestFindSecurityGroupForInstance(t *testing.T) {
+	groups := map[string]*ec2.SecurityGroup{"sg123": {GroupId: aws.String("sg123")}}
+	id, err := findSecurityGroupForInstance(&ec2.Instance{SecurityGroups: []*ec2.GroupIdentifier{{GroupId: aws.String("sg123"), GroupName: aws.String("my_group")}}}, groups)
+	if err != nil {
+		t.Error()
+	}
+	assert.Equal(t, *id.GroupId, "sg123")
+	assert.Equal(t, *id.GroupName, "my_group")
+}
+
+func TestFindSecurityGroupForInstanceMultipleTagged(t *testing.T) {
+	groups := map[string]*ec2.SecurityGroup{"sg123": {GroupId: aws.String("sg123")}}
+	_, err := findSecurityGroupForInstance(&ec2.Instance{
+		SecurityGroups: []*ec2.GroupIdentifier{
+			{GroupId: aws.String("sg123"), GroupName: aws.String("my_group")},
+			{GroupId: aws.String("sg123"), GroupName: aws.String("another_group")},
+		},
+	}, groups)
+	require.Error(t, err)
+	assert.Contains(t, err.Error(), "sg123(my_group)")
+	assert.Contains(t, err.Error(), "sg123(another_group)")
+}
+
 func newMockedFakeAWSServices(id string) *FakeAWSServices {
 	s := NewFakeAWSServices(id)
 	s.ec2 = &MockedFakeEC2{FakeEC2Impl: s.ec2.(*FakeEC2Impl)}