Update to support more regions

Relates https://github.com/hashicorp/terraform/issues/524
Added `eu-central-1`, `cn-north-1` and `us-gove-west-1`(hi NSA)
I checked `goamz`, @mitchellh already has added support for those regions

builtin/providers/aws/config.go

@@ -33,8 +33,9 @@ func (c *Config) AWSAuth() (aws.Auth, error) {
 // IsValidRegion returns true if the configured region is a valid AWS
 // region and false if it's not
 func (c *Config) IsValidRegion() bool {
-	var regions = [8]string{"us-east-1", "us-west-2", "us-west-1", "eu-west-1",
-		"ap-southeast-1", "ap-southeast-2", "ap-northeast-1", "sa-east-1"}
+	var regions = [11]string{"us-east-1", "us-west-2", "us-west-1", "eu-west-1",
+		"eu-central-1", "ap-southeast-1", "ap-southeast-2", "ap-northeast-1",
+		"sa-east-1", "cn-north-1", "us-gov-west-1"}
 
 	for _, valid := range regions {
 		if c.Region == valid {