LDAP: Fetch users and groups using wildcards
    
    Related:
        https://fedorahosted.org/sssd/ticket/2553
    
    Adds handler for the BE_FILTER_WILDCARD in the LDAP provider. So far
    it's the same code as if enumeration was used, so there are no limits.
    
    Reviewed-by: Pavel Březina <pbrezina@redhat.com>