Conditionalize ez_setup

This makes life simpler for packagers, since most packaging tools
will ensure that the appropriate packages are available on the
system. Additionally, most packaging tools prefer not to rely on
network access (since it can mean that identical rebuilds cannot
be performed).

Built locally with 'python setup.py build' and also by applying this
patch and performing an RPM build in a network-free environment.

Reviewed at http://reviews.reviewboard.org/r/3978/