Fix installation of the python bindnings when py-setuptools* is installed.

When py-setuptools is installed, metadata for the python package is handled
differently than when building the package in for instance poudriere. Fix
the python bindings install script to always act the same way, regardless of
setuptools.

PR: 206769
Submitted by: Reid Linnemann <linnemannr@gmail.com>
Reported by: dewayne@heuristicsystems.com.au
Sponsored by: BSDCan 2016 Hackerlounge