Call eglSwapBuffers() to ensure wayland surface is attached

Call eglSwapBuffers() to ensure wayland surface is attached

Resize surface tests initially create a window and a surface, ensure
that both has the same size, then perform a window resize, and ensure
that both windows and the surface has the same size.

When using a Wayland target, checking the window size is done calling
wl_egl_window_get_attached_size(). This actually returns the size of the
attached buffer, which is done calling wl_surface_attach().

But wl_surface_attach() is only guaranteed to be done when calling
eglSwapBuffers(); if wl_egl_window_get_attached_size() is invoked
before, it can return 0, as no buffer is attached yet.

To avoid this problem, ensure a buffer is attached before getting the
window size.

Affects:
dEQP-EGL.functional.resize.surface_size.*

Components: OpenGL

VK-GL-CTS issue: 594

Change-Id: I74fb9a10b269ea1e1f7a63457fb0df76f8604547