provider/aws: Update Redshift SG Acctests

Allows redshift security group tests to better handle being ran in parallel.

```
$ make testacc TEST=./builtin/providers/aws TESTARGS='-run=TestAccAWSRedshiftSecurityGroup_'
==> Checking that code complies with gofmt requirements...
go generate $(go list ./... | grep -v /terraform/vendor/)
2017/02/09 10:40:25 Generated command/internal_plugin_list.go
TF_ACC=1 go test ./builtin/providers/aws -v -run=TestAccAWSRedshiftSecurityGroup_ -timeout 120m
=== RUN   TestAccAWSRedshiftSecurityGroup_importBasic
--- PASS: TestAccAWSRedshiftSecurityGroup_importBasic (12.98s)
=== RUN   TestAccAWSRedshiftSecurityGroup_ingressCidr
--- PASS: TestAccAWSRedshiftSecurityGroup_ingressCidr (11.02s)
=== RUN   TestAccAWSRedshiftSecurityGroup_updateIngressCidr
--- PASS: TestAccAWSRedshiftSecurityGroup_updateIngressCidr (32.81s)
=== RUN   TestAccAWSRedshiftSecurityGroup_ingressSecurityGroup
--- PASS: TestAccAWSRedshiftSecurityGroup_ingressSecurityGroup (14.82s)
=== RUN   TestAccAWSRedshiftSecurityGroup_updateIngressSecurityGroup
--- PASS: TestAccAWSRedshiftSecurityGroup_updateIngressSecurityGroup (37.43s)
PASS
ok      github.com/hashicorp/terraform/builtin/providers/aws    109.090s
```

Author: grubernaut

builtin/providers/aws/import_aws_redshift_security_group_test.go

@@ -4,13 +4,15 @@ import (
 	"os"
 	"testing"
 
+	"github.com/hashicorp/terraform/helper/acctest"
 	"github.com/hashicorp/terraform/helper/resource"
 )
 
 func TestAccAWSRedshiftSecurityGroup_importBasic(t *testing.T) {
 	oldvar := os.Getenv("AWS_DEFAULT_REGION")
 	os.Setenv("AWS_DEFAULT_REGION", "us-east-1")
 	defer os.Setenv("AWS_DEFAULT_REGION", oldvar)
+	rInt := acctest.RandInt()
 
 	resourceName := "aws_redshift_security_group.bar"
 
@@ -19,11 +21,11 @@ func TestAccAWSRedshiftSecurityGroup_importBasic(t *testing.T) {
 		Providers:    testAccProviders,
 		CheckDestroy: testAccCheckAWSRedshiftSecurityGroupDestroy,
 		Steps: []resource.TestStep{
-			resource.TestStep{
-				Config: testAccAWSRedshiftSecurityGroupConfig_ingressCidr,
+			{
+				Config: testAccAWSRedshiftSecurityGroupConfig_ingressCidr(rInt),
 			},
 
-			resource.TestStep{
+			{
 				ResourceName:      resourceName,
 				ImportState:       true,
 				ImportStateVerify: true,