Previously the db_event_subscription import would only work if there was a single db_event_subscription resource. This fixes the import, allowing it to work as expected.
Also fixes the acceptance test for the resource to reflect this.
```
$ make testacc TEST=./builtin/providers/aws TESTARGS='-run=TestAccAWSDBEventSubscription_importBasic'
==> Checking that code complies with gofmt requirements...
go generate $(go list ./... | grep -v /terraform/vendor/)
2017/02/07 10:38:10 Generated command/internal_plugin_list.go
TF_ACC=1 go test ./builtin/providers/aws -v -run=TestAccAWSDBEventSubscription_importBasic -timeout 120m
=== RUN TestAccAWSDBEventSubscription_importBasic
--- PASS: TestAccAWSDBEventSubscription_importBasic (633.33s)
PASS
ok github.com/hashicorp/terraform/builtin/providers/aws 633.353s
```
Jake Champlin