Update information about python version in setup.cfg
Update information about python version in setup.cfg

This patch updates information about python versions written in
setup.cfg, based on the following two points of view.

* Python 2.6 is now not supported by swift.
* Python 3.x may be supported, but not tested yet.

Change-Id: Ic0af191f64e22cb3ec8a055031e7e6c958f10f2a

openstack/storlets,openstack/storlets,openstack/storlets,openstack/storlets