Remove memcache

[benarmston]

• Memcache is no longer used as an interchange, so we don't need to install it, monitor it, configure it, etc..
• With memcache replaced by HTTP request the metric daemon no longer needs Ruby helper scripts.
• Remove the unused installation of systemctl service files in a docker build.
• Finally, combine the misc_packages and appliance-dev roles.

See https://github.com/alces-flight/concertim-ct-visualisation-app/pull/60/ for the corresponding ct visualisation changes.