Previously, string "{0}" was replaced by the user dn in the groups_filter
attributes of the LDAP configuration.
However, if the groups children only have a memberUid attribute, one would
like to use the username instead of the user dn.
Since the user dn can be built from the username, "{0}" is now replaced
by the username instead of the user dn so that an LDAP relying on attribute
'memberUid' can be used.
