Split DUTLink driver to individual pieces to be used from config

[mangelajo]

I have found, that when using and configuring the DUTLink as a composite driver, it's very handy, and works great.

For making demos and explaining jumpstarter it doesn't help. Because the configuration is seen as a big monolithic device and you cannot explain well what's going on.

I want to provide support in DUTLink to configure all the sub devices individually, referencing the S/N of the device in configuration.

[NickCao]

Done in jumpstarter-dev/jumpstarter#221 and jumpstarter-dev/jumpstarter#223