Fix parameter of set_passwd_ldap_user error

login is a string and not an instance of user.

issue4394
review13761003
(grafted from cab8d2b8e6819e150d6d22c94c9a7a896f3f04df)

--HG--
branch : 2.8
extra : source : cab8d2b8e6819e150d6d22c94c9a7a896f3f04df