ui: use pbsUserSelector for BackupGroupChangeOwner

www/BackupGroupChangeOwner.js

@@ -31,8 +31,9 @@ Ext.define('PBS.BackupGroupChangeOwner', {
 
 		column1: [
 		    {
-			xtype: 'textfield',
+			xtype: 'pbsUserSelector',
 			name: 'new-owner',
+			value: me.owner,
 			fieldLabel: gettext('Userid'),
 			minLength: 8,
 			allowBlank: false,

www/datastore/Content.js

@@ -281,6 +281,7 @@ Ext.define('PBS.DataStoreContent', {
 		datastore: view.datastore,
 		backup_type: data.backup_type,
 		backup_id: data.backup_id,
+		owner: data.owner,
 		autoShow: true,
 	    });
 	    win.on('destroy', this.reload, this);