Refactor connectivity intent creation to use builders

- Each connectivity intent now has only one constructor
- Intent constructors are now private for leaf classes and
  protected for classes that can be derived from
- Each intent class has a Builder class that accumulates
  parameters for intent creation
- Each intent class has a public static builder() method
  to create a builder
- Each Builder class has a build() method to create the
  intent from the accumulated parameters
- Added keys to a few intent types that were missing them
- Tightened up usage of checkNotNull(), taking advantage of
  the return value to save some lines of code
- Modified callers to use the builders instead of directly
  calling the constructors

Change-Id: I713185d5ecbadbf51f87ef7f68fec41102106c78
diff --git a/core/net/src/test/java/org/onosproject/net/intent/impl/phase/CompilingTest.java b/core/net/src/test/java/org/onosproject/net/intent/impl/phase/CompilingTest.java
index d450812..a968e4e 100644
--- a/core/net/src/test/java/org/onosproject/net/intent/impl/phase/CompilingTest.java
+++ b/core/net/src/test/java/org/onosproject/net/intent/impl/phase/CompilingTest.java
@@ -97,7 +97,12 @@
                 .ingressPoint(cp1)
                 .egressPoint(cp3)
                 .build();
-        compiled = new PathIntent(appId, selector, treatment, path);
+        compiled = PathIntent.builder()
+                .appId(appId)
+                .selector(selector)
+                .treatment(treatment)
+                .path(path)
+                .build();
     }