monitor/dim_brightness test case is untested in AIO

We have a few options here:

1) Test brightness on all of the machines
2) Try to detect if X exposes the brightness control interface
3) Try to detect if sysfs exposes the brightness control interface
4) Use DMI to check for "AIO" class systems (not sure if DMI supports that)
5) Work on manifests and derive this information from the manifest

dmi.product is somewhat unreliable, another solution (and one which would take care of other issues too) is to come up with a dedicated form_factor resource and map all those disparate DMI types (pizza box is a valid dmi type) into form factors we care about.

Finally, this test should probably depend on having a built-in screen, not on the form factor itself, so we could also try to detect that (e.g. LVDS1 and eDP1 as seen by xrandr are usually built-in screens).

Jerry, could you please run these commands on your AIO and attach the resulting files? (Just so we have an idea of what their data looks like).

sudo dmidecode > dmidecode.log
xrandr -q > xrandr.log

OK, the chassis is :

Handle 0x0003, DMI type 3, 25 bytes
Chassis Information
    Manufacturer: Hewlett-Packard
    Type: All In One
    Lock: Not Present

And the screen is eDP1:

Screen 0: minimum 8 x 8, current 1920 x 1080, maximum 16384 x 16384
eDP1 connected 1920x1080+0+0 509mm x 286mm
VGA1 disconnected
VIRTUAL1 disconnected

So the easy solution which we can implement very quickly is to modify monitor.txt.in and add "All in One" to the list of form factors:

plugin: user-interact-verify
id: monitor/dim_brightness
requires: dmi.product in ['Notebook','Laptop','Portable', 'All In One']

The other solutions, including manifests, requiring a hypothetical new display_type resource:

requires display_type.type == 'Built-in'

and verifying the kernel interfaces Zygmunt mentioned, would require a bit more work.