The egl implementation for the virtual platform tries to use a render
node if available. If there is no render node it looks for a virtual
(kernel driver vgem) device, which unfortunately does not create a
render node in mainline kernel (there are patches in ChromiumOS).
For this the Udev wrapper is extended to search for renderNode devices
and for virtual dri devices.
If either render node or vgem dri device is found, it is tried to be
opened (without logind escalation) and on success a gbm device is
created on it. If any step of this fails the so far default behavior
of default device is tried for creating the EGLDisplay.
All of this is compile optional, so that the virtual platform does not
hard depend on udev and/or gbm.