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/main/java/org/onosproject/net/intent/impl/compiler/MplsIntentCompiler.java b/core/net/src/main/java/org/onosproject/net/intent/impl/compiler/MplsIntentCompiler.java
index 948dbd6..b59d7eb 100644
--- a/core/net/src/main/java/org/onosproject/net/intent/impl/compiler/MplsIntentCompiler.java
+++ b/core/net/src/main/java/org/onosproject/net/intent/impl/compiler/MplsIntentCompiler.java
@@ -75,11 +75,16 @@
      */
     private Intent createPathIntent(Path path,
                                     MplsIntent intent) {
-        return new MplsPathIntent(intent.appId(),
-                              intent.selector(), intent.treatment(), path,
-                              intent.ingressLabel(), intent.egressLabel(),
-                              intent.constraints(),
-                              intent.priority());
+        return MplsPathIntent.builder()
+                .appId(intent.appId())
+                .selector(intent.selector())
+                .treatment(intent.treatment())
+                .path(path)
+                .ingressLabel(intent.ingressLabel())
+                .egressLabel(intent.egressLabel())
+                .constraints(intent.constraints())
+                .priority(intent.priority())
+                .build();
     }