Updates aws_rds_cluster acceptance tests to use ARN testing check functions
Updates aws_rds_cluster acceptance tests to use ARN testing check functions

Addresses:
aws/resource_aws_rds_cluster_test.go:117:6: AWSAT001: prefer resource.TestCheckResourceAttrPair() or ARN check functions (e.g. testAccMatchResourceAttrRegionalARN)

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