add ca-central-1 to list of known aws regions.

resolves #4273

builder/amazon/common/regions.go

@@ -1,5 +1,6 @@
 package common
 
+// aws ec2 describe-regions --query 'Regions[].{Name:RegionName}' --output text | sed 's/\(.*\)/"\1",/' | sort
 func listEC2Regions() []string {
 	return []string{
 		"ap-northeast-1",
@@ -7,15 +8,17 @@ func listEC2Regions() []string {
 		"ap-south-1",
 		"ap-southeast-1",
 		"ap-southeast-2",
-		"cn-north-1",
+		"ca-central-1",
 		"eu-central-1",
 		"eu-west-1",
 		"sa-east-1",
 		"us-east-1",
 		"us-east-2",
-		"us-gov-west-1",
 		"us-west-1",
 		"us-west-2",
+		// not part of autogenerated list
+		"us-gov-west-1",
+		"cn-north-1",
 	}
 }