This test overrides the AWS_DEFAULT_REGION parameter as the security
groups are created in us-east-1 (due to classic VPC requirements)
```
% make testacc TEST=./builtin/providers/aws TESTARGS='-run=TestAccAWSDBSecurityGroup_importBasic'
==> Checking that code complies with gofmt requirements...
go generate $(go list ./... | grep -v /terraform/vendor/)
TF_ACC=1 go test ./builtin/providers/aws -v
-run=TestAccAWSDBSecurityGroup_importBasic -timeout 120m
=== RUN TestAccAWSDBSecurityGroup_importBasic
--- PASS: TestAccAWSDBSecurityGroup_importBasic (49.46s)
PASS
ok github.com/hashicorp/terraform/builtin/providers/aws 49.487s
```