Update rack_maint.inc.php permission

Modify permission to increase control and utility.
Need add 3 new permissions with dcm.pl, else you can always used it like before
dcm.pl order:
./dcm.pl -r add_permission name=rack_add desc='show rack'
./dcm.pl -r add_permission name=rack_mod desc='modify rack'
./dcm.pl -r add_permission name=rack_del desc='delete rack'

it's used at my work