Get rid of openstack.common.py3kcompat

py3kcompat was removed from oslo-incubator because everything it
provided was already in six version we depend on (see oslo-incubator
change I06b90f789ae21f2ef8b8071b4298bfc0406482a6). So we should
use six for urlparse, too.

Change-Id: I0ab7119c985c247c2f701e3bb6b16353cf7399f0