arb_framebuffer: Test clearing of incomplete framebuffer

From OpenGL 4.6, section 9.4.4 "Effects of Framebuffer Completeness on
Framebuffer Operations", page 332:

"An INVALID_FRAMEBUFFER_OPERATION error is generated by attempts to render
to or read from a framebuffer which is not framebuffer complete.
This error is generated regardless of whether fragments are actually read
from or written to the framebuffer. For example, it is generated when a
rendering command is called and the framebuffer is incomplete, even if
RASTERIZER_DISCARD is enabled."

Test that glClear*buffer functions generate INVALID_FRAMEBUFFER_OPERATION
when trying to clear an incomplete framebuffer. To do this, we create an
incomplete framebuffer, try to clear it and check if
INVALID_FRAMEBUFFER_OPERATION is generated, then we make the buffer complete
and clear again, the second clearing should be successful.

This test is created to test a regression
mesa/mesa#2072, it was caused by
testing buffer's completeness in clearing function before updating
the completeness state of a buffer.

Signed-off-by: Dmytro Nester <dmytro.nester@globallogic.com>
Status Job ID Name Coverage
  Container
passed debian #2413921

00:00:19

 
  Build
passed build #2413922

00:05:19

passed py.test #2413923

00:00:28

passed tox #2413924

00:02:36