[AETHER-1104] Calculate PiPipeconf fingerprint in a deterministic way

New master after taking over a switch was pushing again the pipeline
and all the flows and groups. This was happening because DefaultPiPipeconf
fingerprint was not calculated in a deterministic way across the cluster.

This patch introduces the following changes:
- Implements toString method in each abstraction representing a pipeline
- Hashes the p4Info file to generate a consistent hash of the pipeline model
- Uses a sorted collection to generate a consistent hash of the extensions

Change-Id: I792283b0a9b821284add36b3aba52843f33527c3
diff --git a/protocols/p4runtime/model/src/main/java/org/onosproject/p4runtime/model/P4ControlMetadataModel.java b/protocols/p4runtime/model/src/main/java/org/onosproject/p4runtime/model/P4ControlMetadataModel.java
index a6e2a43..19a6fa7 100644
--- a/protocols/p4runtime/model/src/main/java/org/onosproject/p4runtime/model/P4ControlMetadataModel.java
+++ b/protocols/p4runtime/model/src/main/java/org/onosproject/p4runtime/model/P4ControlMetadataModel.java
@@ -21,6 +21,8 @@
 
 import java.util.Objects;
 
+import static com.google.common.base.MoreObjects.toStringHelper;
+
 /**
  * Implementation of PiPacketMetadataModel for P4Runtime.
  */
@@ -61,4 +63,12 @@
         return Objects.equals(this.id, other.id)
                 && Objects.equals(this.bitWidth, other.bitWidth);
     }
+
+    @Override
+    public String toString() {
+        return toStringHelper(this)
+                .add("id", id)
+                .add("bitWidth", bitWidth)
+                .toString();
+    }
 }