setup.py should properly package versioninfo

setup.py was putting the versioninfo file in two places:

$ sudo python setup.py install --root=/tmp/kc
*snip*
$ find /tmp/kc -name versioninfo
/tmp/kc/usr/keystoneclient/versioninfo
/tmp/kc/usr/lib/python2.6/site-packages/keystoneclient/versioninfo

By using package_data rather than data_files in setup.py the versioninfo
file is only put in the pythonlib dir.