Async netconf API + command for netconf troubleshooting

- Added async API for fetching entire config (+ state)
- netconf-get
   issue netcong rpc get
- netconf-get-config
   Revised to use async API to deal with slow device

Example usage:
  onos> netconf-get netconf:192.168.56.1:2022 | ppxml

 for ONOS-7481

Change-Id: Id012e984275109c93bdae113f3fec685a7b2211b
diff --git a/protocols/netconf/ctl/src/main/java/org/onosproject/netconf/cli/impl/NetconfGetCommand.java b/protocols/netconf/ctl/src/main/java/org/onosproject/netconf/cli/impl/NetconfGetCommand.java
new file mode 100644
index 0000000..2d29fcd
--- /dev/null
+++ b/protocols/netconf/ctl/src/main/java/org/onosproject/netconf/cli/impl/NetconfGetCommand.java
@@ -0,0 +1,80 @@
+/*
+ * Copyright 2016-present Open Networking Foundation
+ *
+ * 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.netconf.cli.impl;
+
+import static com.google.common.base.Preconditions.checkNotNull;
+import java.util.concurrent.ExecutionException;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.TimeoutException;
+
+import org.apache.karaf.shell.commands.Argument;
+import org.apache.karaf.shell.commands.Command;
+import org.apache.karaf.shell.commands.Option;
+import org.onosproject.cli.AbstractShellCommand;
+import org.onosproject.net.DeviceId;
+import org.onosproject.netconf.NetconfController;
+import org.onosproject.netconf.NetconfDevice;
+import org.onosproject.netconf.NetconfException;
+import org.onosproject.netconf.NetconfSession;
+
+/**
+ * Command that retrieves running configuration and device state.
+ * If configuration cannot be retrieved it prints an error string.
+ */
+@Command(scope = "onos", name = "netconf-get",
+        description = "Retrieve running configuration and "
+                + "device state information from specified device.")
+public class NetconfGetCommand extends AbstractShellCommand {
+
+    @Argument(index = 0, name = "deviceId", description = "Device ID",
+            required = true, multiValued = false)
+    String uri = null;
+
+    @Option(name = "--timeout",
+            description = "Timeout in seconds",
+            required = false)
+    long timeoutSec = 30;
+
+    @Override
+    protected void execute() {
+        DeviceId deviceId = DeviceId.deviceId(uri);
+
+        NetconfController controller = get(NetconfController.class);
+        checkNotNull(controller, "Netconf controller is null");
+
+        NetconfDevice device = controller.getDevicesMap().get(deviceId);
+        if (device == null) {
+            print("Netconf device object not found for %s", deviceId);
+            return;
+        }
+
+        NetconfSession session = device.getSession();
+        if (session == null) {
+            print("Netconf session not found for %s", deviceId);
+            return;
+        }
+
+        try {
+            CharSequence res = session.asyncGet()
+                    .get(timeoutSec, TimeUnit.SECONDS);
+            print("%s", res);
+        } catch (NetconfException | InterruptedException | ExecutionException | TimeoutException e) {
+            log.error("Configuration could not be retrieved", e);
+            print("Error occurred retrieving configuration");
+        }
+    }
+
+}