keyring: Align some srtings to right in RTL

https://bugzilla.gnome.org/show_bug.cgi?id=712594

data/theme/gnome-shell.css

@@ -2095,6 +2095,10 @@ StScrollBar StButton#vhandle:active {
     color: #666666;
 }
 
+.prompt-dialog-description:rtl {
+    text-align: right;
+}
+
 .prompt-dialog-password-box {
     spacing: 1em;
     padding-bottom: 1em;

js/ui/components/keyring.js

@@ -45,7 +45,9 @@ const KeyringDialog = new Lang.Class({
         this.prompt.bind_property('message', subject, 'text', GObject.BindingFlags.SYNC_CREATE);
 
         this._messageBox.add(subject,
-                             { y_fill:  false,
+                             { x_fill: false,
+                               y_fill:  false,
+                               x_align: St.Align.START,
                                y_align: St.Align.START });
 
         let description = new St.Label({ style_class: 'prompt-dialog-description' });