Use VK_REMAINING_MIP_LEVELS in image clearing tests

Use VK_REMAINING_MIP_LEVELS in image clearing tests

Modified tests:
- dEQP-VK.api.image_clearing.clear_color_image.*
- dEQP-VK.api.image_clearing.* (refactor)

Tests were refactored to use images with more than one mip map,
but multiple mip maps were only added to clear_color_image tests.

Image is now cleared with two distinct colors, one for explicit
range of mip maps, the other for VK_REMAINING_MIP_LEVELS.

Fixes #459

Change-Id: Ia02289bf81faebd47c2e4c86a6bd8a4d06ddf34d