[NO ISSUE][OTH] Fix ActiveEntityEventsListener toString

- user model changes: no
- storage format changes: no
- interface changes: no

Details:
- Return proper JSON from ActiveEntityEventsListener toString.

Change-Id: Ifd31bfa71eb79cf4f292c3453cb66523dfba261e
Reviewed-on: https://asterix-gerrit.ics.uci.edu/3219
Sonar-Qube: Jenkins <jenkins@fulliautomatix.ics.uci.edu>
Integration-Tests: Jenkins <jenkins@fulliautomatix.ics.uci.edu>
Tested-by: Jenkins <jenkins@fulliautomatix.ics.uci.edu>
Contrib: Jenkins <jenkins@fulliautomatix.ics.uci.edu>
Reviewed-by: Ali Alsuliman <ali.al.solaiman@gmail.com>
diff --git a/asterixdb/asterix-app/src/main/java/org/apache/asterix/app/active/ActiveEntityEventsListener.java b/asterixdb/asterix-app/src/main/java/org/apache/asterix/app/active/ActiveEntityEventsListener.java
index 783d823..3b847b3 100644
--- a/asterixdb/asterix-app/src/main/java/org/apache/asterix/app/active/ActiveEntityEventsListener.java
+++ b/asterixdb/asterix-app/src/main/java/org/apache/asterix/app/active/ActiveEntityEventsListener.java
@@ -687,7 +687,7 @@
 
     @Override
     public String toString() {
-        return "{\"class\":\"" + getClass().getSimpleName() + "\"" + "\"entityId\":\"" + entityId + "\""
+        return "{\"class\":\"" + getClass().getSimpleName() + "\"," + "\"entityId\":\"" + entityId + "\","
                 + "\"state\":\"" + state + "\"" + "}";
     }
 }