Bug#23072792 MYSQL_GROUP_SUFFIX DOES NOT WORK

Reintroduce environment variable MYSQL_GROUP_SUFFIX to be used as
--default-group-suffix value if not already set.

The environment variable was accidentally renamed to DEFAULT_GROUP_SUFFIX_ENV
in MySQL server 5.5.

mysys/default.c

-/* Copyright (c) 2000, 2011, Oracle and/or its affiliates. All rights reserved.
+/* Copyright (c) 2000, 2017, Oracle and/or its affiliates. All rights reserved.
 
    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -234,7 +234,7 @@ int my_search_option_files(const char *conf_file, int *argc, char ***argv,
                                     (char **) &my_defaults_group_suffix);
 
   if (! my_defaults_group_suffix)
-    my_defaults_group_suffix= getenv(STRINGIFY_ARG(DEFAULT_GROUP_SUFFIX_ENV));
+    my_defaults_group_suffix= getenv("MYSQL_GROUP_SUFFIX");
 
   if (forced_extra_defaults && !defaults_already_read)
   {