Allow table-less selects even when wsrep is not ready

It doesn't make sense to allow selects from I_S but disallow selects
that don't use any tables at all, because any (disallowed) select that
doesn't use tables can be made allowed by adding
"FROM I_S.COLLATIONS LIMIT 1" to the end.

And it break mysql-test rather badly, even check-testcase.test
fails on its first `SELECT '$tmp' = 'No such row'`

This reverts 9a89614, c5dd2ab, and 33028f7:
Refs: MW-245 - changed logic so that in non primary node it is possible to do SET + SHOW + SELECT from information and pfs schema, when dirty reads are not enabled - however, non table selects are not allowed (e.g. SELECT 1)
Refs MW-245 - logic was wrong in detecting if queries are allowed in non primary node. it allowed select with no table list to execute even if dirty reads was not specified
Refs: MW-245 - Adjust tests to account for the new behavior.

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

@@ -30,9 +30,9 @@ SET @@session.wsrep_dirty_reads=OFF;
 SELECT i, variable_name, variable_value FROM t1, information_schema.session_variables WHERE variable_name LIKE "wsrep_dirty_reads" AND i = 1;
 ERROR 08S01: WSREP has not yet prepared node for application use
 SELECT 1;
-ERROR 08S01: WSREP has not yet prepared node for application use
+1
+1
 USE information_schema;
-ERROR 08S01: WSREP has not yet prepared node for application use
 SELECT * FROM information_schema.session_variables WHERE variable_name LIKE "wsrep_dirty_reads";
 VARIABLE_NAME	VARIABLE_VALUE
 WSREP_DIRTY_READS	OFF

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

@@ -51,7 +51,7 @@ INSERT INTO t1 VALUES (1),(2),(3),(4),(5);
 --let $value = query_get_value(SHOW SLAVE STATUS, Last_SQL_Error, 1)
 --connection node_3
 --disable_query_log
---eval SELECT "$value" IN ("Error 'WSREP has not yet prepared node for application use' on query. Default database: 'test'. Query: 'BEGIN'", "Node has dropped from cluster") AS expected_error
+--eval SELECT "$value" IN ("Error 'Unknown command' on query. Default database: 'test'. Query: 'BEGIN'", "Node has dropped from cluster") AS expected_error
 --enable_query_log
 
 # Step #4. Bring back the async slave and restart replication
@@ -85,9 +85,8 @@ DROP TABLE t1;
 STOP SLAVE;
 RESET SLAVE ALL;
 
-CALL mtr.add_suppression("Slave SQL: Error 'WSREP has not yet prepared node for application use' on query");
-CALL mtr.add_suppression("Slave: WSREP has not yet prepared node for application use Error_code: 1047");
-CALL mtr.add_suppression("TORDERED} returned -107 \\(Transport endpoint is not connected\\)");
+CALL mtr.add_suppression("Slave SQL: Error 'Unknown command' on query");
+CALL mtr.add_suppression("Slave: Unknown command Error_code: 1047");
 CALL mtr.add_suppression("Transport endpoint is not connected");
 CALL mtr.add_suppression("Slave SQL: Error in Xid_log_event: Commit could not be completed, 'Deadlock found when trying to get lock; try restarting transaction', Error_code: 1213");
 CALL mtr.add_suppression("Slave SQL: Node has dropped from cluster, Error_code: 1047");

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

@@ -47,10 +47,8 @@ SET @@session.wsrep_dirty_reads=OFF;
 --error ER_UNKNOWN_COM_ERROR
 SELECT i, variable_name, variable_value FROM t1, information_schema.session_variables WHERE variable_name LIKE "wsrep_dirty_reads" AND i = 1;
 
---error ER_UNKNOWN_COM_ERROR
 SELECT 1;
 
---error ER_UNKNOWN_COM_ERROR
 USE information_schema;
 
 SELECT * FROM information_schema.session_variables WHERE variable_name LIKE "wsrep_dirty_reads";

sql/sql_parse.cc

@@ -893,7 +893,6 @@ void cleanup_items(Item *item)
 #ifdef WITH_WSREP
 static bool wsrep_tables_accessible_when_detached(const TABLE_LIST *tables)
 {
-  bool has_tables = false;
   for (const TABLE_LIST *table= tables; table; table= table->next_global)
   {
     TABLE_CATEGORY c;
@@ -906,9 +905,8 @@ static bool wsrep_tables_accessible_when_detached(const TABLE_LIST *tables)
     {
       return false;
     }
-    has_tables = true;
   }
-  return has_tables;
+  return true;
 }
 #endif /* WITH_WSREP */
 #ifndef EMBEDDED_LIBRARY