Added CLI to flush flow rules installed by cordvtn

Might be useful to refresh data plane with most recent status of Neutron
and VMs by flushing all existing rules and pushing network config again
And also removed read configuration during activation since leadership
service does not work as expected during app activation

Change-Id: Ia22fe02d25a61126f3e6df59fc5ad4d065f89f18
diff --git a/apps/cordvtn/src/main/java/org/onosproject/cordvtn/CordVtnRuleInstaller.java b/apps/cordvtn/src/main/java/org/onosproject/cordvtn/CordVtnRuleInstaller.java
index f3877e0..808f7c6 100644
--- a/apps/cordvtn/src/main/java/org/onosproject/cordvtn/CordVtnRuleInstaller.java
+++ b/apps/cordvtn/src/main/java/org/onosproject/cordvtn/CordVtnRuleInstaller.java
@@ -172,6 +172,13 @@
     }
 
     /**
+     * Flush flows installed by this application.
+     */
+    public void flushRules() {
+        flowRuleService.getFlowRulesById(appId).forEach(flowRule -> processFlowRule(false, flowRule));
+    }
+
+    /**
      * Populates basic rules that connect a VM to the other VMs in the system.
      *
      * @param host host