Decouple the seleniumrunner from the browser and the xserver.

Provides the xserver and the firefox hook.

seleniumrunner code (inside the recipe) still has to be merged with its
original code to prevent duplication.

Allows to run firefox with a new profile each time to prevent having session
conflict.

It allows to start a X server inside a slapos instance.
Provide an hook to do a screenshot of the X session.

Use the TMPDIR environment variable to define the location of files created by
xorg.

It allows to cleanly run X application in any slapos instance.

It allows to directly control firefox from supervisord if needed.

Use slapos provided libraries by defined include and rpath

I just lost time because error was not explicit nor helpful.