Update get_attr_filter in LDAPSearch to handle nsaccountlock user searches
    
    - Update get_attr_filter in LDAPSearch to handle nsaccountlock by setting the default value for
      nsaccountlock to false as well as update the filter to check for the default value
    - Remove pytest xfail for test_find_enabled_user
    
    https://pagure.io/freeipa/issue/6896
    
    Reviewed-By: Jan Cholasta <jcholast@redhat.com>