tests/resource/aws_s3_bucket_notification: Refactor for concurrency and add Lambda Alias test
tests/resource/aws_s3_bucket_notification: Refactor for concurrency and add Lambda Alias test

Reference:

* https://github.com/terraform-providers/terraform-provider-aws/issues/5930

Changes:

* Replace serialized _importBasic and _basic acceptance tests with parallelized tests
* Add Lambda Alias test
* Simplify randomized naming to single variable

Output from acceptance testing:

```
--- PASS: TestAccAWSS3BucketNotification_LambdaFunction (42.65s)
--- PASS: TestAccAWSS3BucketNotification_LambdaFunction_LambdaFunctionArn_Alias (34.78s)
--- PASS: TestAccAWSS3BucketNotification_Queue (33.96s)
--- PASS: TestAccAWSS3BucketNotification_Topic (34.50s)
--- PASS: TestAccAWSS3BucketNotification_Topic_Multiple (36.83s)
--- PASS: TestAccAWSS3BucketNotification_update (54.90s)
```

Ninir/terraform-provider-aws,terraform-providers/terraform-provider-aws,kjmkznr/terraform-provider-aws,terraform-providers/terraform-provider-aws,Ninir/terraform-provider-aws,terraform-providers/terraform-provider-aws,kjmkznr/terraform-provider-aws,Ninir/terraform-provider-aws,kjmkznr/terraform-provider-aws,Ninir/terraform-provider-aws,kjmkznr/terraform-provider-aws,terraform-providers/terraform-provider-aws