- Fix useradd invocation: -o is useless without -u and newer
versions of pwdutils/shadowutils fail on this now.

- Implement a multi-instance setup
* Allow for multiple configuration files of named instances
under /etc/redis
* Each instance has its own data directory
under /var/lib/redis/$INSTANCE
* Each instance has its own PID file
under /var/run/redis/$INSTANCE.pid
* Each instance has its own log files
under /var/log/redis/$INSTANCE.log
* Instances may be started or stopped individually passing a
second argument to the init script
* Do not create an active default.conf, rather use an
.example suffix