Add support for using init.d instead of upstart

[organicveggie]

Since upstart is not standard on RHEL flavors of Linux, this provides more typical support for using init.d. Controlled via an attribute that defaults to using upstart.

[jakedavis]

Could we make this something like default[:exhibitor][:supervisor] = 'upstart'?

[jakedavis]

Hiya, thanks for the PR. I dropped a few notes in; @whilp and @mwhooker in particular might have more. This is looking good, and we're keen to get cross-platform support in our cookbooks. A few tweaks should put this in a ready to go state.

[webframp]

Always great to see a PR, but based on some experience it can grow unwieldy to manage init scripts. This is why we often default to runit (when possible)

[whilp]

We also prefer runit for most stuff we write. @organicveggie would runit help get you going on non-upstart systems? If so, we might as well just switch over to that completely.