Refactor UPF entities to have consistent naming and string representations

Also, add slice ID into applications and interfaces entities

Change-Id: I159bcf04af1504b4e5c7210aa1402218fae3eb8f
(cherry picked from commit de1f1f7806716ac6e368e55eaf0b887ab89530d4)
diff --git a/core/api/src/main/java/org/onosproject/net/behaviour/upf/UpfTerminationUplink.java b/core/api/src/main/java/org/onosproject/net/behaviour/upf/UpfTerminationUplink.java
index 1c6dd56..93ac0b7 100644
--- a/core/api/src/main/java/org/onosproject/net/behaviour/upf/UpfTerminationUplink.java
+++ b/core/api/src/main/java/org/onosproject/net/behaviour/upf/UpfTerminationUplink.java
@@ -129,7 +129,7 @@
 
     @Override
     public String toString() {
-        return "TerminationUL{" + matchString() + " -> " + actionString() + "}";
+        return "UpfTerminationUL(" + matchString() + " -> " + actionString() + ")";
     }
 
     private String matchString() {
@@ -141,9 +141,9 @@
         if (this.needsDropping()) {
             fwd = "DROP";
         }
-        return "(" + fwd +
-                ", CTR_ID=" + this.counterId() +
-                ", TC=" + this.trafficClass() +
+        return "Action(" + fwd +
+                ", ctr_id=" + this.counterId() +
+                ", tc=" + this.trafficClass() +
                 ")";
     }