Fix issue with depulicate ssh keys after save

The CloudConfig.Save() did not load the metadata resulting in the diff
function always thinking the SSH keys were new.  This would cause them
to be saved over and over again just getting bigger and bigger.

config/config.go

@@ -163,6 +163,9 @@ func (c *CloudConfig) Save() error {
 	if err != nil {
 		return err
 	}
+
+	exCfg = mergeMetadata(exCfg, readMetadata())
+
 	exData := map[interface{}]interface{}{}
 	if err := util.Convert(exCfg, &exData); err != nil {
 		return err