Fixed MDEV-8428: Mangled DML statements on 2nd level slave when enabling binlog checksums

Fix was to add a test in Query_log_event::Query_log_event() if we are using
CREATE ... SELECT and in this case use trans cache, like we do on the master.
This avoid using (with doesn't have checksum)

Other things:
- Removed dummy call my_checksum(0L, NULL, 0)
- More DBUG_PRINT
- Cleaned up Log_event::need_checksum() to make it more readable (similar as in MySQL 5.6)
- Renamed variable that was hiding another one in create_table_imp()

sql/sql_table.cc

@@ -4684,12 +4684,12 @@ int create_table_impl(THD *thd,
       bool table_creation_was_logged= tmp_table->s->table_creation_was_logged;
       if (create_info->options & HA_LEX_CREATE_REPLACE)
       {
-        bool is_trans;
+        bool tmp;
         /*
           We are using CREATE OR REPLACE on an existing temporary table
           Remove the old table so that we can re-create it.
         */
-        if (drop_temporary_table(thd, tmp_table, &is_trans))
+        if (drop_temporary_table(thd, tmp_table, &tmp))
           goto err;
       }
       else if (create_info->options & HA_LEX_CREATE_IF_NOT_EXISTS)