python-pyudev: upgrade to 0.16.1 and fix some issues

* RDEPENDing on libudev always selects udev as provider (even when systemd
  should be used), for details see:
  https://bugzilla.yoctoproject.org/show_bug.cgi?id=3622


* don't import pyudev from setup.py to get right pyudev version, this does
  not work without pyudev installed

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>