rename plugin null_audit -> audit_null (to match status variable names)

create audit_null.test

mysql-test/suite/plugins/r/audit_null.result

+set @old_global_general_log=@@global.general_log;
+set global general_log=OFF;
+install plugin audit_null soname 'adt_null';
+select 1;
+1
+1
+select foobar;
+ERROR 42S22: Unknown column 'foobar' in 'field list'
+show status like 'audit_null%';
+Variable_name	Value
+Audit_null_called	6
+Audit_null_general_error	1
+Audit_null_general_log	0
+Audit_null_general_result	2
+uninstall plugin audit_null;
+Warnings:
+Warning	1620	Plugin is busy and will be uninstalled on shutdown
+set global general_log=@old_global_general_log;

mysql-test/suite/plugins/t/audit_null.test

+if (!$ADT_NULL_SO) {
+  skip No NULL_AUDIT plugin;
+}
+
+set @old_global_general_log=@@global.general_log;
+set global general_log=OFF;
+
+install plugin audit_null soname 'adt_null';
+
+select 1;
+--error 1054
+select foobar;
+show status like 'audit_null%';
+
+uninstall plugin audit_null;
+
+set global general_log=@old_global_general_log;
+

plugin/audit_null/audit_null.c

@@ -145,7 +145,7 @@ mysql_declare_plugin(audit_null)
 {
   MYSQL_AUDIT_PLUGIN,         /* type                            */
   &audit_null_descriptor,     /* descriptor                      */
-  "NULL_AUDIT",               /* name                            */
+  "AUDIT_NULL",               /* name                            */
   "Oracle Corp",              /* author                          */
   "Simple NULL Audit",        /* description                     */
   PLUGIN_LICENSE_GPL,