Use the new oslo.cache library instead of using memcached directly.
This keeps the old options around and will continue to use those in
preference to the oslo.config library as there is no way to test whether
oslo.cache was explicitly configured to use that in preference.
Currently there are no messages or anything to deprecate the old options
until we've had a chance to test it in production environments.
Closes-Bug: #1523375
Change-Id: Ifccacc5db311ad538ce60191cbe221644d1a5807
Co-Authored-By: Nicolas Helgeson <nh202b@att.com>
9d8e2836fe