install xorg void input driver
Set default resolution to 1280x1024 in xorg.conf

We set this in xorg.conf instead of resizing using xrandr, to avoid
fonts resize problems.

This does not remove the problem for resolution defined in each test
(currently not used). To fix that, we may need to start a specific X
server for the test.
Make it possible to define enable-tests as an hash ref
Add the --disable-tests option
Disable 3 mochitest-chrome tests

For some unknown reason, those tests are blocking and never finish.