MDEV-11016 wsrep_node_is_ready() check is too strict

      Problem:-
      The condition that checks for node readiness is too strict as it does
      not allow SELECTs even if these selects do not access any tables.
      For example,if we run
           SELECT 1;
      OR
           SELECT @@max_allowed_packet;
      Solution:-
      We need not to report this error when all_tables(lex->query_tables)
      is NULL:

mysql-test/suite/galera/r/galera_var_dirty_reads.result

@@ -18,6 +18,19 @@ SET @@session.wsrep_dirty_reads=ON;
 SELECT * FROM t1;
 i
 1
+SET @@session.wsrep_dirty_reads=OFF;
+SELECT 2;
+2
+2
+SELECT @@max_allowed_packet;
+@@max_allowed_packet
+4194304
+SELECT 2+2 from DUAL;
+2+2
+4
+SELECT sysdate() from DUAL;
+sysdate()
+2016-10-28 23:13:06
 SELECT * FROM t1;
 i
 1

mysql-test/suite/galera/t/galera_var_dirty_reads.test

@@ -39,6 +39,13 @@ SET @@session.wsrep_dirty_reads=ON;
 
 SELECT * FROM t1;
 
+#Select query which does not access table should be allowed MDEV-11016
+SET @@session.wsrep_dirty_reads=OFF;
+SELECT 2;
+SELECT @@max_allowed_packet;
+SELECT 2+2 from DUAL;
+SELECT sysdate() from DUAL;
+
 --disable_query_log
 --eval SET @@global.wsrep_cluster_address = '$wsrep_cluster_address_saved'
 --enable_query_log

sql/sql_parse.cc

@@ -2388,11 +2388,15 @@ mysql_execute_command(THD *thd)
     /*
       Bail out if DB snapshot has not been installed. We however,
       allow SET and SHOW queries.
+      SHOW and SELECT queries (only if wsrep_dirty_reads is set or when it
+      does not access any table).
     */
     if (thd->variables.wsrep_on && !thd->wsrep_applier && !wsrep_ready &&
         lex->sql_command != SQLCOM_SET_OPTION &&
         !(thd->variables.wsrep_dirty_reads &&
           lex->sql_command == SQLCOM_SELECT) &&
+        !(lex->sql_command == SQLCOM_SELECT &&
+          !all_tables)                      &&
         !wsrep_is_show_query(lex->sql_command))
     {
 #if DIRTY_HACK