While we wait for oslo.cache to land, I'd like to maintain a
verbatim copy under marconi.common so that we can start using
it immediately.
When oslo.cache is approved upstream, this copy of the code
will go away and we will add cache to marconi's
openstack-commong.conf
Change-Id: I608a2891ca06caec47ce18eda4edacd07bec40e9
7a7771b06e