When nautilus is automatically tests we cannot assume there is a
display, if we do and we run inside a displayless scenario nautilus
cannot run the application and the tests fail.

Graphical tests were enabled by default, but this breaks most common
automatic tests scenarios, so let's disable it by default and let the
developers enable if required.

We should focus more in unit testing and integration tests without an
actual display, and let tools like OpenQA, etc. to handle actual display
testing. Alternatively we can use Xvfb to simulate a graphical env.