Added management instance handler and some refactoring

- Added management instance handler to provide management network
  connectivity for the management network connected instance, currenly
  local managemenet network connectivity provided
- Renamed Dummy service to Default service
- Renamed CordVtnInstanceHandler to AbstractInstanceHandler and moved
  default VTN rule populations to DefaultInstanceHandler
- Removed workaround management network access code from OLT agent
  instance handler

Change-Id: I990c29b8ae41674d136fbc12f3c4e92167c8c74c
diff --git a/src/main/java/org/opencord/cordvtn/impl/CordVtnInstanceManager.java b/src/main/java/org/opencord/cordvtn/impl/CordVtnInstanceManager.java
index 6acca13..bb5e067 100644
--- a/src/main/java/org/opencord/cordvtn/impl/CordVtnInstanceManager.java
+++ b/src/main/java/org/opencord/cordvtn/impl/CordVtnInstanceManager.java
@@ -82,9 +82,8 @@
 import static java.util.concurrent.Executors.newSingleThreadScheduledExecutor;
 import static org.onlab.util.Tools.groupedThreads;
 import static org.onosproject.dhcp.IpAssignment.AssignmentStatus.Option_RangeNotEnforced;
-import static org.onosproject.xosclient.api.VtnService.NetworkType.MANAGEMENT;
-import static org.onosproject.xosclient.api.VtnService.NetworkType.PRIVATE;
-
+import static org.onosproject.xosclient.api.VtnServiceApi.NetworkType.MANAGEMENT;
+import static org.onosproject.xosclient.api.VtnServiceApi.NetworkType.PRIVATE;
 import static org.slf4j.LoggerFactory.getLogger;
 
 /**