Work toward ONOS-1451: Separate Event Key space per instance

Misc changes and cleanup:
* Added new class OnosInstanceId
* Replace (as appropriate) the string controllerId (and associated methods)
  with the new class OnosInstanceId
* Renaming: Host -> Device
  - Method getDeviceID -> getHostID
  - Changed Host Key ID prefix 'D' to 'H'
  - Few renaming of Host -> Device inside Javadoc

Change-Id: I59c20d68277ecde2f7df4e7097a4a52d5786df1b
diff --git a/src/main/java/net/onrc/onos/core/topology/MastershipEvent.java b/src/main/java/net/onrc/onos/core/topology/MastershipEvent.java
index 5ed36a3..5668e2f 100644
--- a/src/main/java/net/onrc/onos/core/topology/MastershipEvent.java
+++ b/src/main/java/net/onrc/onos/core/topology/MastershipEvent.java
@@ -7,6 +7,7 @@
 import net.floodlightcontroller.core.IFloodlightProviderService.Role;
 import net.onrc.onos.core.topology.web.serializers.MastershipEventSerializer;
 import net.onrc.onos.core.util.Dpid;
+import net.onrc.onos.core.util.OnosInstanceId;
 
 import org.apache.commons.lang.Validate;
 import org.codehaus.jackson.map.annotate.JsonSerialize;
@@ -22,7 +23,7 @@
 public class MastershipEvent extends TopologyElement<MastershipEvent> {
 
     private final Dpid dpid;
-    private final String onosInstanceId;
+    private final OnosInstanceId onosInstanceId;
     private final Role role;
 
     /**
@@ -42,7 +43,8 @@
      * @param onosInstanceId the ONOS Instance ID
      * @param role the ONOS instance role for the switch.
      */
-    public MastershipEvent(Dpid dpid, String onosInstanceId, Role role) {
+    public MastershipEvent(Dpid dpid, OnosInstanceId onosInstanceId,
+                           Role role) {
         Validate.notNull(dpid);
         Validate.notNull(onosInstanceId);
 
@@ -77,7 +79,7 @@
      *
      * @return the ONOS Instance ID.
      */
-    public String getOnosInstanceId() {
+    public OnosInstanceId getOnosInstanceId() {
         return onosInstanceId;
     }