controller: fix debug message (not everytime failed)
multi-bind mode

This mode will multiply the one BIND_DN an try with every
combination of the elements containing "/".

This way it can try for users in all groups:
    cn={user.name},ou=boss/developer,dc=example,dc=com
will try two bind_dn's:
    cn={user.name},ou=boss,dc=example,dc=com
and
    cn={user.name},ou=developer,dc=example,dc=com