Allow apps to leverage CONFIG_FILE

[Ton Brouwer]

iron.io offers the ability to associated config files with code. This would allow for a clean way to pass additional configuration to a task (e.g., change the logging level without a re-deployment).

For this to work, the CONFIG_FILE environment variable must be exposed to the application. It is unclear if this is currently the case.

[Ton Brouwer]

Update: The environment variable is already passed to the app! I found it to be CONFIG_FILE=/mnt/task/config.
So no code changes necessary.