Read CSV from file.

[TTeubler]

Get device list CSV from file. This is a fall-back if the devicelist-* scripts/programs do not work.

[danbim]

I just implemented a cleaner way to achieve this behavior, therefore I'm closing the pull request.

For more information please see:

• https://github.com/itm/testbed-runtime/issues/395
• https://github.com/itm/testbed-runtime/wiki/Testbed-Runtime-0.9#device-autodetection
• https://github.com/itm/testbed-runtime/wiki/Testbed-Runtime-0.9#static-device-configuration