rackspace abandon stack op and unit test
diff --git a/rackspace/orchestration/v1/stacks/delegate.go b/rackspace/orchestration/v1/stacks/delegate.go
index 9c01daf..03557c9 100644
--- a/rackspace/orchestration/v1/stacks/delegate.go
+++ b/rackspace/orchestration/v1/stacks/delegate.go
@@ -37,3 +37,8 @@
 func Preview(c *gophercloud.ServiceClient, opts os.PreviewOptsBuilder) os.PreviewResult {
 	return os.Preview(c, opts)
 }
+
+// Abandon abandons a stack, keeping the resources available.
+func Abandon(c *gophercloud.ServiceClient, stackName, stackID string) os.AbandonResult {
+	return os.Abandon(c, stackName, stackID)
+}