install proper packages

Signed-off-by: Steven Armstrong <steven@icarus.ethz.ch>
python-software-properties still needed for older ubuntu versions

Signed-off-by: Steven Armstrong <steven@icarus.ethz.ch>
Merge branch 'issue/271' of git://github.com/asteven/cdist
++changes

Signed-off-by: Nico Schottelius <nico@bento.schottelius.org>