External window EGL/QT/GLFW test are failing without X server

[Meakk]

Failure with QT is expected because it uses xcb platform by default.
Using an alternative platform like eglfs should work, but I couldn't make it work yet.

Failure with GLFW is expected too and it seems like it's possible to use EGL or OSMesa, but only if GLFW support for these platforms is enabled at compile-time.

Regarding EGL failure, it's passing locally on my side, so it needs more investigation.

To Reproduce
Steps to reproduce the behavior:

1. Stops the X server
2. Run tests TestSDKExternalWindowGLFW, TestSDKExternalWindowQT and TestSDKExternalWindowEGL