Added ability to force mastership re-balancing between instances from the GUI.

Change-Id: I98e56deb3e2b00df630ed85b596c8e35b3d6efab
diff --git a/web/gui/src/main/webapp/topo.js b/web/gui/src/main/webapp/topo.js
index 6673b28..4018757 100644
--- a/web/gui/src/main/webapp/topo.js
+++ b/web/gui/src/main/webapp/topo.js
@@ -140,6 +140,7 @@
         equals: injectStartupEvents,
         dash: injectTestEvent,
 
+        E: [equalizeMasters, 'Equalize mastership roles'],
         O: [toggleSummary, 'Toggle ONOS summary pane'],
         I: [toggleInstances, 'Toggle ONOS instances pane'],
         D: [toggleDetails, 'Disable / enable details pane'],
@@ -926,6 +927,11 @@
         updateDeviceColors();
     }
 
+    function equalizeMasters() {
+        flash('Equalizing master roles');
+        sendMessage('equalizeMasters');
+    }
+
     function toggleSummary() {
         if (!summaryPane.isVisible()) {
             requestSummary();