Add -x option to graphite.rb plugin to allow complex queries with graphite functions

[jennytoo]

This is a simple patch which adds a new option, -x / --complex_target, which disables splitting the target on commas, thus allowing complex targets which contain functions with multiple parameters.

A censored example showing how useSeriesAbove can be used to only alert when a server has been up at least 1200 seconds:

plugins/graphite/graphite.rb -h graphite.example -t 'nonNegativeDerivative(useSeriesAbove(example.server*.uptime, 1200, "uptime", "requests"))' -a 1,1 -g -x
Graphite CRITICAL: The average value of metric nonNegativeDerivative(example.server1.requests) is 372162.7358490566 that is greater than allowed average of 1
The average value of metric nonNegativeDerivative(example.server2.requests) is 220345.547008547 that is greater than allowed average of 1

[jennytoo]

The three failing checks are in files I've not touched. One is an easy fix, but I don't know what to do about the others - there's already rubocop disable statements on both of them and rubocop on my system is honoring them. I'd guess the version of rubocop being used is using a different name for the checks that are alerting.

[jennytoo]

Okay, alternate form of the existing disable check fixed it, plus fixed up a fourth rubocop error that my copy was reporting.

[jennytoo]

It turns out someone else also opened a pull request, #1228, to fix the rubocop errors but it hasn't been merged yet.

[jennytoo]

It looks like this has been moved to sensu-plugins/sensu-plugins-graphite, so I've created sensu-plugins/sensu-plugins-graphite#13 against that repo.