Add tests for GL_EXT_copy_image.

Add tests for GL_EXT_copy_image.

New tests that test GL_EXT_copy_image extension. Tests copy between all
possible format combinations except two float formats. For each format
combination all image target combinations are tested. These tests
always use npot image sizes and npot copy sizes. Offset to source and
destination image is also always npot. When testing texture images,
mipmap complete textures are used and source and destination mipmap
level is always 1. Each test case first tests copying between images
after rendering them to screen and then tests copying between images
immediately after creating them.

Change-Id: If961728d0257109a8cbd97ef8380dd9d89320ecd