IPA/AD/LDAP: Increase the initgrExpireTimestamp after finishing refresh request
    
    Related: https://pagure.io/SSSD/sssd/issue/4012
    
    Calls sysdb_set_initgr_expire_timestamp() after each successfull refresh
    of initgroups data to make sure the initgrExpireTimestamp attribute is
    increased.
    
    If you're wondering why the timestamp is not set by the initgroups operation
    itself, see tickets #3744 or #2634 for examples of bugs caused by setting
    the initgrExpireTimestamp too soon.
    
    Reviewed-by: Sumit Bose <sbose@redhat.com>