MINOR: hlua_fcn: add Patref:add_bulk()

MINOR: hlua_fcn: add Patref:add_bulk()

There is no cli equivalent for this one. It is similar to Patref:add()
excepts thay it takes a table as parameter (for acl: table of keys, for
maps: table of keys:values). The goal is to add multiple entries at once
to limit locking time to the strict minimum. It is recommended to use this
one over Patref:add() when adding multiple entries at once.