users: Set the right toolbar-style on the inline toolbar

While running in a bare X server, I noticed the inline toolbar here
showing its labels, while all the other inline toolbars in other panels
stayed nice and icon-only. The reason is that they explicitly set the
toolbar-style to 'icons'. Do the same here.

https://bugzilla.gnome.org/show_bug.cgi?id=678157

panels/user-accounts/data/user-accounts-dialog.ui

@@ -82,6 +82,7 @@
                         <property name="visible">True</property>
                         <property name="icon_size">1</property>
                         <property name="icon_size_set">True</property>
+                        <property name="toolbar_style">icons</property>
                         <style>
                           <class name="inline-toolbar"/>
                         </style>