Memcached Role in Fedora Server 23

[Stephen Gallagher]

At this week's Fedora Server SIG meeting, I indicated that things were
looking bleak for landing the containerized memcached role in F23. It
turns out things weren't as bad as I feared (with some caveats).

I was able to find the time this week (mostly by turning off IRC) to
get the memcached role built. It's not the final version I was hoping
for (producing a nulecule app), but it *can* serve memcached using the
official Fedora Dockerfiles version of the service uploaded to the
Docker Hub.

What do I need help with?
 * I need someone to run through the open code review requests[1]. I
think things are in good shape, but I would prefer a second set of eyes
on them.


So, what can it do right now?
 * You can deploy a memcached role entirely on the local machine, the
same way that you can deploy the database server role or the domain
controller role.
 * You can deploy the role with no arguments (it has sensible
defaults).
 * You can pass arguments to control the cache size, number of
connections and number of threads.
 * You can pass a special boolean argument "contained". This will cause
the role to be deployed by pulling down the fedora/memcached image from
Docker Hub and creating a systemd unit file to load it at boot.

Caveats:
 * The containerized version is just that; memcached in a container. It
has no advanced orchestration capabilities.
 * The version of the fedora/memcached image in the Docker Hub doesn't
have the capability to tune the same values as the local version. Right
now, these are ignored. I have a pull request[1] open to fix this.



[1] https://reviewboard-fedoraserver.rhcloud.com/r/
[2] https://github.com/fedora-cloud/Fedora-Dockerfiles/pull/115