provider/aws: Rename the Import aws_opsworks_stack import test

The casing on the test name was causing it not to run with the entire
test suite

```
% make testacc TEST=./builtin/providers/aws
% TESTARGS='-run=TestAccAWSOpsworksStack'             2 ↵ ✹
==> Checking that code complies with gofmt requirements...
go generate $(go list ./... | grep -v /terraform/vendor/)
2016/10/03 16:43:07 Generated command/internal_plugin_list.go
TF_ACC=1 go test ./builtin/providers/aws -v -run=TestAccAWSOpsworksStack
-timeout 120m
=== RUN   TestAccAWSOpsworksStackImportBasic
--- PASS: TestAccAWSOpsworksStackImportBasic (49.00s)
=== RUN   TestAccAWSOpsworksStackNoVpc
--- PASS: TestAccAWSOpsworksStackNoVpc (36.10s)
=== RUN   TestAccAWSOpsworksStackVpc
--- PASS: TestAccAWSOpsworksStackVpc (73.27s)
PASS
ok      github.com/hashicorp/terraform/builtin/providers/aws158.385s
```

builtin/providers/aws/import_aws_opsworks_stack_test.go

@@ -1,18 +1,13 @@
 package aws
 
 import (
-	"os"
 	"testing"
 
 	"github.com/hashicorp/terraform/helper/acctest"
 	"github.com/hashicorp/terraform/helper/resource"
 )
 
-func TestAccAWSOpsWorksStack_importBasic(t *testing.T) {
-	oldvar := os.Getenv("AWS_DEFAULT_REGION")
-	os.Setenv("AWS_DEFAULT_REGION", "us-west-2")
-	defer os.Setenv("AWS_DEFAULT_REGION", oldvar)
-
+func TestAccAWSOpsworksStackImportBasic(t *testing.T) {
 	name := acctest.RandString(10)
 
 	resourceName := "aws_opsworks_stack.tf-acc"