Add missing helperClassNames for mongo drivers 3.1 and 3.4

Author: na-ji

dd-java-agent/instrumentation/mongo/driver-3.1/src/main/java/datadog/trace/instrumentation/mongo/MongoClient31Instrumentation.java

@@ -57,6 +57,8 @@ public String[] helperClassNames() {
       packageName + ".MongoDecorator",
       packageName + ".MongoDecorator31",
       packageName + ".Context",
+      packageName + ".MongoCommentInjector",
+      "datadog.trace.core.database.SharedDBCommenter",
       packageName + ".MongoCommandListener",
       packageName + ".MongoCommandListener$SpanEntry"
     };

dd-java-agent/instrumentation/mongo/driver-3.4/src/main/java/datadog/trace/instrumentation/mongo/MongoClient34Instrumentation.java

@@ -69,6 +69,8 @@ public String[] helperClassNames() {
       packageName + ".MongoDecorator",
       packageName + ".MongoDecorator34",
       packageName + ".Context",
+      packageName + ".MongoCommentInjector",
+      "datadog.trace.core.database.SharedDBCommenter",
       packageName + ".MongoCommandListener",
       packageName + ".MongoCommandListener$SpanEntry"
     };