Memcached Improvements

Improvements to memcached:
- Make the following memcached variables configurable
    * port
    * pid file
    * max slab size
    * max memory usage (can be set by AWS instance type)

- Add security group for memcached port

- Change name of memcached user from 'nobody' to 'memcache' as per Ubuntu standard (see: https://bugs.launchpad.net/ubuntu/+source/memcached/+bug/599461)

- Add stop/start/restart/status actions for memcached

- Added Dalli config to share memcached between all instances

- Deleted memcached.yml (it is obsolete and not used by Dalli)

- Merge branch 'monit-memcached' of matsu911/rubber (refer to PR #303)