Minor improvement dealing with Port

- include annotations in DefaultPort#toString()
- add method to retrieve a Port using ConnectPoint

Change-Id: I75f24e53235f46fa8deeb62b55bec2ecafae907c
diff --git a/core/api/src/main/java/org/onosproject/net/DefaultPort.java b/core/api/src/main/java/org/onosproject/net/DefaultPort.java
index 85e2de1..70023cc 100644
--- a/core/api/src/main/java/org/onosproject/net/DefaultPort.java
+++ b/core/api/src/main/java/org/onosproject/net/DefaultPort.java
@@ -121,6 +121,7 @@
                 .add("isEnabled", isEnabled)
                 .add("type", type)
                 .add("portSpeed", portSpeed)
+                .add("annotations", annotations())
                 .toString();
     }