PYCBC-243: iops/select: Use rich comparison methods rather than __cmp__

This fixes an issue where tests would fail under Python 3. The __cmp__
method is not used in Python 3, which rather expects to find the rich
comparison operations
(https://docs.python.org/2/reference/datamodel.html#object.__lt__)

Change-Id: I4c0cdb3d7bd96bbefdec58e65ddc2b382acca458
Reviewed-on: http://review.couchbase.org/37083
Tested-by: Mark Nunberg <mnunberg@haskalah.org>
Reviewed-by: Volker Mische <volker.mische@gmail.com>