Add keys to intents

- use Key class rather than String for intent keys
- add CLI option to specify a string key
- add key field to constructors for connectivity intents
- translate id into a key if no key is specified

Change-Id: I69ffbad93bc3daddf06a67cb0cffa2130e781b37
diff --git a/core/api/src/main/java/org/onosproject/net/intent/IntentOperation.java b/core/api/src/main/java/org/onosproject/net/intent/IntentOperation.java
index 7eed841..ef16a69 100644
--- a/core/api/src/main/java/org/onosproject/net/intent/IntentOperation.java
+++ b/core/api/src/main/java/org/onosproject/net/intent/IntentOperation.java
@@ -73,7 +73,12 @@
         return intent.id();
     }
 
-    public String key() {
+    /**
+     * Returns the key for this intent.
+     *
+     * @return key value
+     */
+    public Key key() {
         return intent.key();
     }