MDEV-12017 Unclear error with flashback: Variable 'binlog_format' can't ...

When WSREP(thd) is not true we will use my_error(...) to print error. This
will set thd->is_error() to true and we wont be getting generic error.
Signed-off-by: Sachin Setiya <sachin.setiya@mariadb.com>

mysql-test/suite/binlog/r/flashback.result

@@ -502,4 +502,8 @@ a	b
 2	1
 3	2
 4	3
+SET binlog_format=statement;
+ERROR HY000: Flashback does not support binlog_format STATEMENT
+SET GLOBAL binlog_format=statement;
+ERROR HY000: Flashback does not support binlog_format STATEMENT
 DROP TABLE t1;

mysql-test/suite/binlog/t/flashback.test

@@ -160,4 +160,9 @@ let $MYSQLD_DATADIR= `select @@datadir`;
 
 SELECT * FROM t1;
 
+--error ER_FLASHBACK_NOT_SUPPORTED
+SET binlog_format=statement;
+--error ER_FLASHBACK_NOT_SUPPORTED
+SET GLOBAL binlog_format=statement;
+
 DROP TABLE t1;

sql/share/errmsg-utf8.txt

@@ -7453,3 +7453,5 @@ ER_JSON_PATH_EMPTY
         eng "Path expression '$' is not allowed in argument %d to function '%s'."
 ER_SLAVE_SAME_ID
         eng "A slave with the same server_uuid/server_id as this slave has connected to the master"
+ER_FLASHBACK_NOT_SUPPORTED
+        eng "Flashback does not support %s %s"

sql/sys_vars.cc

@@ -456,13 +456,13 @@ static bool binlog_format_check(sys_var *self, THD *thd, set_var *var)
     push_warning_printf(thd, Sql_condition::WARN_LEVEL_WARN, ER_UNKNOWN_ERROR,
                         "MariaDB Galera and flashback do not support binlog format: %s",
                         binlog_format_names[var->save_result.ulonglong_value]);
-
-    if (var->type == OPT_GLOBAL)
-    {
-      WSREP_ERROR("MariaDB Galera and flashback do not support binlog format: %s",
+    if (WSREP(thd))
+      WSREP_ERROR("MariaDB Galera does not support binlog format: %s",
                   binlog_format_names[var->save_result.ulonglong_value]);
-      return true;
-    }
+    else
+      my_error(ER_FLASHBACK_NOT_SUPPORTED,MYF(0),"binlog_format",
+                binlog_format_names[var->save_result.ulonglong_value]);
+    return true;
   }
 
   if (var->type == OPT_GLOBAL)