Unit tests for some Intent objects and compilers

Unit tests for HostToHost and MultiPointToSinglePoint intents
and intent compilers.

Made Intent classes final to make them immutable.
diff --git a/core/api/src/main/java/org/onlab/onos/net/intent/MultiPointToSinglePointIntent.java b/core/api/src/main/java/org/onlab/onos/net/intent/MultiPointToSinglePointIntent.java
index be8d309..8ee4a9e 100644
--- a/core/api/src/main/java/org/onlab/onos/net/intent/MultiPointToSinglePointIntent.java
+++ b/core/api/src/main/java/org/onlab/onos/net/intent/MultiPointToSinglePointIntent.java
@@ -15,7 +15,7 @@
 /**
  * Abstraction of multiple source to single destination connectivity intent.
  */
-public class MultiPointToSinglePointIntent extends ConnectivityIntent {
+public final class MultiPointToSinglePointIntent extends ConnectivityIntent {
 
     private final Set<ConnectPoint> ingressPoints;
     private final ConnectPoint egressPoint;