Track session autocommit state

This tracks only what is explicitly set. That is, if autocommit
has been set true then, even if a transaction is started, autocommit
will not be set false.

That is, a user of the session autocommit and transaction states
need to be aware of their semantics. If a transaction is active,
then the state of autocommit is irrelevant.

server/modules/protocol/MySQL/MySQLClient/mysql_client.c

@@ -916,6 +916,14 @@ gw_read_finish_processing(DCB *dcb, GWBUF *read_buffer, uint64_t capabilities)
         {
             session_set_trx_state(ses, SESSION_TRX_INACTIVE);
         }
+        else if (type & QUERY_TYPE_ENABLE_AUTOCOMMIT)
+        {
+            session_set_autocommit(ses, true);
+        }
+        else if (type & QUERY_TYPE_DISABLE_AUTOCOMMIT)
+        {
+            session_set_autocommit(ses, false);
+        }
 
         /**
          * Feed each statement completely and separately