Munin contributed plugins

Ruby plugins: apply style changes as suggested by "rubocop --fix-layout"

Reduce number of categories
riak -> other (riak)
smf -> forum (smf)
reddit -> other (reddit)
sge -> htc (sge)
netscaler -> loadbalancer (netscaler)
nutcracker -> other (twemproxy)
requesttracker -> other (requesttracker)
passenger -> webserver (passenger)...