add proxy support

[kam1kaze]

Hi,

We need a proxy support of this plugin. Unfortunately, It looks like we cannot implement such feature until jaxxstorm/redphone#9 pull request is merged to redphone library.

[analytically]

We're not using redphone anymore.

[masteinhauser]

It looks like HTTP Proxy support is not supported within the pagerduty gem when comparing to the Ruby Docs for Net::HTTP and how to use Proxies.

I might be able to provide a PR for this, but we are evaluating using flapjack.io instead of hitting PagerDuty's API directly anyway.

[orien]

FYI the Pagerduty gem now has an explicit API for configuring an HTTP proxy. Version 2.1.0 has been released with this feature.

envato/pagerduty#47

[willejs]

I was using this plugin with the http/s proxy environment variables defined and im 99.9% sure it worked?

[masteinhauser]

@willejs I don't remember exactly what lead me to my conclusion, but it also highly depends on which version of Ruby you are running sensu and the handler under.

[willejs]

Ive got the code somewhere where i did this, I remember playing around with this for a while. Essentially, you need to make sure the proxy_server variables are set in the parent process that spawns ruby.
Let me double check.

[eheydrick]

Proxy support was added in #26 by @lcrisci and released in version 2.0.0 which is now on Rubygems.