Non-portable tests

[Marckvdv]

Some tests depend on functions that may work differently on different machines. One of these functions is: Texture2d::empty and other functions like this one which don't specify a specific pixel format.

2 of these test are:

uniforms_storage_ignore_inactive_uniforms uniforms_storage_single_value

I'm pretty sure there are more of these, though I will try to add them later.