Fix window size issues in several new tests

Fix window size issues in several new tests

Some of the new tests added in the last 6 months fail when run with
non-default window sizes. In two cases, the tests were hardcoded to use
64x64 without checking the underlying size and thus could end up
with corruption if the window size was smaller.

In another case, the test changes the framebuffer to zero mid-test
instead of to the default framebuffer, resulting in invalid results
with deqp-surface-type=fbo.

Finally, the generated texture data's alpha is intended to always
be 1.0, but it can vary slightly due to numerical instability
depending on the window size. It is now hardcoded to ensure we
get the intended result.

VK-GL-CTS issue: 1126

Components: OpenGL

Affects:
KHR-GL*.internalformat.renderbuffer.*
KHR-GL*.internalformat.texture2d.*
KHR-GLES*.shaders.aggressive_optimizations.*

Change-Id: I3c1779cc7818ba5b1a798ec683af2780eeb9c9f4