Adding a grid topology simulator to the null provider.

Change-Id: Ie655840febc11d3986f1c8ec5c8ef2374014794c
diff --git a/providers/null/src/main/java/org/onosproject/provider/nil/cli/NullDeviceCommand.java b/providers/null/src/main/java/org/onosproject/provider/nil/cli/NullDeviceCommand.java
new file mode 100644
index 0000000..00bc5b9
--- /dev/null
+++ b/providers/null/src/main/java/org/onosproject/provider/nil/cli/NullDeviceCommand.java
@@ -0,0 +1,57 @@
+/*
+ * Copyright 2016 Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.onosproject.provider.nil.cli;
+
+import org.apache.karaf.shell.commands.Argument;
+import org.apache.karaf.shell.commands.Command;
+import org.onosproject.cli.AbstractShellCommand;
+import org.onosproject.net.DeviceId;
+import org.onosproject.provider.nil.NullProviders;
+
+import static org.onosproject.cli.UpDownCompleter.DOWN;
+import static org.onosproject.cli.UpDownCompleter.UP;
+
+/**
+ * Servers or repairs a simulated link.
+ */
+@Command(scope = "onos", name = "null-device",
+        description = "Severs or repairs a simulated link")
+public class NullDeviceCommand extends AbstractShellCommand {
+
+    @Argument(index = 0, name = "id", description = "Device identifier",
+            required = true, multiValued = false)
+    String id = null;
+
+    @Argument(index = 1, name = "cmd", description = "up/down",
+            required = true, multiValued = false)
+    String cmd = null;
+
+
+    @Override
+    protected void execute() {
+        NullProviders service = get(NullProviders.class);
+        DeviceId deviceId = DeviceId.deviceId(id);
+
+        if (cmd.equals(UP)) {
+            service.repairDevice(deviceId);
+        } else if (cmd.equals(DOWN)) {
+            service.failDevice(deviceId);
+        } else {
+            error("Illegal command %s; must be up or down", cmd);
+        }
+    }
+
+}