Code review comment for lp:~dpigott/lava-dispatcher/add-sdmux-support

My only concern is that this will remove bootloader support from beaglebone-black. As all the master image devices are now using client_type = bootloader. This is not a big deal, I'll approve the merge, but lets work together to find a way that master / bootloader/ and sdmux can use the same client_type.

I would recommend rebasing these changes on the tip before the merge, in case their are any conflicts LP is not picking up.

* Do you want the power_on_cmd and power_off_cmd to be defined in that manner?