fix-issue-150

This patch fixes issue RedHatQE#150 changing
work_item.py get_custom_fields method return code
from : None
to : cls._all_custom_fields, cls._required_fields

Signed-off-by: Eli Mesika <emesika@redjat.com>

src/pylero/work_item.py

@@ -1468,7 +1468,7 @@ def get_custom_fields(cls, project_id):
             if cft.required:
                 cls._required_fields.append(local_name)
         cls._got_custom_fields = True
-        return None
+        return cls._all_custom_fields, cls._required_fields
 
     @classmethod
     def query(