Disable Skylight when running in development environment

[JonRCahill]

Skylight currently runs in all environments even when a blank SKYLIGHT_AUTHENTICATION has been set. The biggest issue this causes is that shutting down the Phoenix server will take 1 min when integrated with Skylight. This additionally affects running tests with mix test if the server option has been enabled.

Happy to do this myself if I can be pointed to the best way to disable Skylight.

[wagenet]

Thanks for catching this. The Ruby gem won't boot the native agent if there isn't a token, we should do the same here. Also, it should be possible to have the shutdown not block on the native daemon. The daemon won't shut down immediately but after a little bit will realize it's not getting anything from the main app and shut down on its own.