git-remote-testpy: hash bytes explicitly

git-remote-testpy: hash bytes explicitly

Under Python 3 'hasher.update(...)' must take a byte string and not a
unicode string.  Explicitly encode the argument to this method to hex
bytes so that we don't need to worry about failures to encode that might
occur if we chose a textual encoding.

This changes the directory used by git-remote-testpy for its git mirror
of the remote repository, but this tool should not have any serious
users as it is used primarily to test the Python remote helper
framework.

The use of encode() moves the required Python version forward to 2.0.

Signed-off-by: John Keeping <john@keeping.me.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>