Make return type from urlsplit private

The ModifiedSplitResult class should be private because when we drop
python 2.6 support we can replace the urlsplit() wrapper we have with a
reference to the one in the python standard library, which returns a
different type.

Change-Id: I413de125c58ee54a0aaaf608f57283e76283bf84
Merge "Make return type from urlsplit private"