Hello, thanks for the answer
I have tried and spent a long time trying to run the tests with Xvfb, but it did not work, so we install the gnome, and we get around this problem.
We managed to work around the problem mentioned above, was not the most elegant solution unfortunately, but it was not for lack of trying.
To run the selenium tests, the gnome must be active (an logged in user). So we set up the gnome to on boot, do not ask password, and never turn off the display screen. And as result we have a accessible Xorg/X11, even for SSH calls.
To run the selenium server we create a shell script, which combined with crontab, reboot the selenium server every midnight. (I heard that it gives problems if used for a long time without turning off).
I am over two weeks working on it, I tried to use the plugins of selenium and Xvfb in jenkins, but nothing worked, the only way I could do it all run, is controlling the selenium server and X11/Xorg outside jenkins. X11 using the gnome. I am frustrated by spending so much time and in the end, the things are working in the wrong way, BUT THE MOST IMPORTANT: we now have a continuous integration server running.
Thank you, and we can close the topic.