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
```
It seems there are 4 locations left that use the `helper/multierror`
package, where the rest is TF settled on the `hashicorp/go-multierror`
package.
Functionally this doesn’t change anything, so I suggest to delete the
builtin version as it can only cause confusion (both packages have the
same name, but are still different types according to Go’s type system.
This landed in aws-sdk-go yesterday, breaking the AWS provider in many places:
3c259c9586
Here, with much sedding, grepping, and manual massaging, we attempt to
catch Terraform up to the new `awserr.Error` interface world.
stack72