core: fix calls to domish.Element.elements:

domish.Element.elements should be called with namespace and element name as 2 arguments,
but it has been confused in several places with the call to `domish.Element.addElement`
which is often done with a `(namespace, name)` tuple. Unfortunately calling with a tuple
is accepted and doesn't raise any error in `elements`, but this result in a wrong element
returned.

This patch fixes the erroneous calls.

sat/plugins/plugin_comp_file_sharing.py

@@ -731,7 +731,7 @@ class FileSharing:
     def _getDirectoryMetadataElts(
             self, client, elt, file_data):
         try:
-            affiliation_elt = next(elt.elements((NS_FS_AFFILIATION, "affiliation")))
+            affiliation_elt = next(elt.elements(NS_FS_AFFILIATION, "affiliation"))
         except StopIteration:
             pass
         else: