Bug fix : add check befor fencing

plugins/hypervisors/kvm/src/main/java/org/apache/cloudstack/kvm/ha/KVMHAProvider.java

@@ -35,6 +35,7 @@
 import org.apache.cloudstack.outofbandmanagement.OutOfBandManagement.PowerOperation;
 import org.apache.cloudstack.outofbandmanagement.OutOfBandManagementService;
 import org.joda.time.DateTime;
+import com.cloud.host.Status;
 
 import javax.inject.Inject;
 
@@ -84,11 +85,17 @@
 
     @Override
     public boolean fence(Host r) throws HAFenceException {
-
         try {
-            if (outOfBandManagementService.isOutOfBandManagementEnabled(r)){
-                final OutOfBandManagementResponse resp = outOfBandManagementService.executePowerOperation(r, PowerOperation.OFF, null);
-                return resp.getSuccess();
+            // host exists and is managed OOB
+            if (r != null && outOfBandManagementService.isOutOfBandManagementEnabled(r)) {
+                // check host status
+                if (Status.Down.equals(r.getStatus())) {
+                    logger.info("Host " + r.getName() + " is already down. Returning success.");
+                    return true;
+                } else {
+                    final OutOfBandManagementResponse resp = outOfBandManagementService.executePowerOperation(r, PowerOperation.OFF, null);
+                    return resp.getSuccess();
+                }
             } else {
                 logger.warn("OOBM fence operation failed for this host " + r.getName());
                 return false;