add String method to AbandonResult
diff --git a/openstack/orchestration/v1/stacks/results.go b/openstack/orchestration/v1/stacks/results.go
index 1e60f8a..3d0d75e 100644
--- a/openstack/orchestration/v1/stacks/results.go
+++ b/openstack/orchestration/v1/stacks/results.go
@@ -1,6 +1,7 @@
 package stacks
 
 import (
+	"encoding/json"
 	"time"
 
 	"github.com/mitchellh/mapstructure"
@@ -283,3 +284,11 @@
 
 	return &res, nil
 }
+
+func (r AbandonResult) String() (string, error) {
+	out, err := json.Marshal(r)
+	if err != nil {
+		return "", err
+	}
+	return string(out), nil
+}