Take down edge ports on a leaf switch when all uplinks are gone

- Bug fix for case when all uplinks are gone, but dual-homed host continues to send packets to switch;
  We now administratively take down the host port to force the host to use the other leaf in the pair.
- Restructured SR manager by creating a LinkHandler
- fixed/added some log messages

Change-Id: I3722cd364dc8798b16891519bec165627e92bd87
diff --git a/src/test/java/org/onosproject/segmentrouting/MockLinkHandler.java b/src/test/java/org/onosproject/segmentrouting/MockLinkHandler.java
new file mode 100644
index 0000000..2819c9d
--- /dev/null
+++ b/src/test/java/org/onosproject/segmentrouting/MockLinkHandler.java
@@ -0,0 +1,36 @@
+/*
+ * Copyright 2017-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.segmentrouting;
+
+import org.onosproject.net.HostLocation;
+
+/**
+ * Mocks the LinkHandler in SR.
+ *
+ */
+public class MockLinkHandler extends LinkHandler {
+
+    MockLinkHandler(SegmentRoutingManager srManager) {
+        super(srManager, null);
+    }
+
+    @Override
+    void checkUplinksForDualHomedHosts(HostLocation loc) {
+        // currently does nothing - can be extended to be a useful mock when
+        // implementing unit tests for link handling
+    }
+}