Allows the redshift parameter group acceptance tests handle being ran in parallel better
```
$ make testacc TEST=./builtin/providers/aws TESTARGS='-run=TestAccAWSRedshiftParameterGroup_'
==> Checking that code complies with gofmt requirements...
go generate $(go list ./... | grep -v /terraform/vendor/)
2017/02/09 10:16:19 Generated command/internal_plugin_list.go
TF_ACC=1 go test ./builtin/providers/aws -v -run=TestAccAWSRedshiftParameterGroup_ -timeout 120m
=== RUN TestAccAWSRedshiftParameterGroup_importBasic
--- PASS: TestAccAWSRedshiftParameterGroup_importBasic (15.17s)
=== RUN TestAccAWSRedshiftParameterGroup_withParameters
--- PASS: TestAccAWSRedshiftParameterGroup_withParameters (13.16s)
=== RUN TestAccAWSRedshiftParameterGroup_withoutParameters
--- PASS: TestAccAWSRedshiftParameterGroup_withoutParameters (12.58s)
PASS
ok github.com/hashicorp/terraform/builtin/providers/aws 40.940s
```