FIX don't strickly check for graphics bus

src/validate.lua

@@ -141,7 +141,8 @@ local validate_filesystem = function(x)
 end
 
 local validate_graphics = function(x)
-   M.assert_file_readable('graphics.dev_power', x.dev_power)
+   -- NOTE don't check that the bus exists because some optimus laptops 'turn
+   -- off' by pulling the entire kernel module and making the bus go poof
    M.validate_plot_ticks_y('graphics.geometry', x.geometry.plot.ticks_y)
 end