Merge branch 'issue_72' into 'master'

Several fixes for pipeline.sampler.image_view tests

Fix mapping of VK filter modes to Sampler::filter modes. Fix LOD calculation for VK_SAMPLER_MIPMAP_MODE_BASE. Adjust texcoords to avoid tiebreaking rules. Clamp lodMid to .01 for minfilter tests. Disable linear filtering tests for integer formats.

See #72 and #74.

See merge request !142

diff --cc external/vulkancts/framework/vulkan/vkImageUtil.cpp
Simple merge

diff --cc external/vulkancts/modules/vulkan/pipeline/vktPipelineImageSamplingInstance.cpp
Simple merge