tests/resource/aws_datapipeline_pipeline: Add PreCheck for service availability
tests/resource/aws_datapipeline_pipeline: Add PreCheck for service availability

Output from acceptance testing in AWS Commercial:

```
--- PASS: TestAccAWSDataPipelinePipeline_disappears (9.82s)
--- PASS: TestAccAWSDataPipelinePipeline_description (18.86s)
--- PASS: TestAccAWSDataPipelinePipeline_basic (18.89s)
--- PASS: TestAccAWSDataPipelinePipeline_tags (23.33s)
PASS
```

Output from acceptance testing in AWS GovCloud (US):

```
--- SKIP: TestAccAWSDataPipelinePipeline_description (1.57s)
    resource_aws_datapipeline_pipeline_test.go:230: skipping acceptance testing: RequestError: send request failed
        caused by: Post https://datapipeline.us-gov-west-1.amazonaws.com/: dial tcp: lookup datapipeline.us-gov-west-1.amazonaws.com: no such host
--- SKIP: TestAccAWSDataPipelinePipeline_disappears (1.57s)
    resource_aws_datapipeline_pipeline_test.go:230: skipping acceptance testing: RequestError: send request failed
        caused by: Post https://datapipeline.us-gov-west-1.amazonaws.com/: dial tcp: lookup datapipeline.us-gov-west-1.amazonaws.com: no such host
--- SKIP: TestAccAWSDataPipelinePipeline_basic (1.57s)
    resource_aws_datapipeline_pipeline_test.go:230: skipping acceptance testing: RequestError: send request failed
        caused by: Post https://datapipeline.us-gov-west-1.amazonaws.com/: dial tcp: lookup datapipeline.us-gov-west-1.amazonaws.com: no such host
--- SKIP: TestAccAWSDataPipelinePipeline_tags (1.57s)
    resource_aws_datapipeline_pipeline_test.go:230: skipping acceptance testing: RequestError: send request failed
        caused by: Post https://datapipeline.us-gov-west-1.amazonaws.com/: dial tcp: lookup datapipeline.us-gov-west-1.amazonaws.com: no such host
PASS
```

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