ceph-deploy: implement --version

Version number is stamped into package's distutils information,
which is stored in egg-info/PKG-INFO.  It's initialized from either

 * an envvar set in debian/rules by parsing debian/changelog, or
 * a local git-describe (if this package is set up with virtualenv)

Signed-off-by: Dan Mick <dan.mick@inktank.com>
Try to make .spec set version in the 'standard' way