taskserver/helpertool: Fix error message on export

The error message displays that a specific user doesn't exist in an
organisation, but uses the User object's name attribute to show which
user it was.

This is basically a very stupid chicken and egg problem and easily fixed
by using the user name provided on the command line.

Signed-off-by: aszlig <[e-mail]>

nixos/modules/services/misc/taskserver/helper-tool.py

···
     userobj = organisation.get_user(user)
     if userobj is None:
         msg = "User {} doesn't exist in organisation {}."
-        sys.exit(msg.format(userobj.name, organisation.name))
+        sys.exit(msg.format(user, organisation.name))
 
     sys.stdout.write(userobj.export())