Reduce number of created pipelines in compute subgroups tests

Reduce number of created pipelines in compute subgroups tests

Some drivers are taking too much time to execute compute subgroups
tests, mostly because they need to build N times the same pipeline
where the only difference is the local size values passed via
specialization constants.

As there are drivers that don't take advantage of pipeline derivatives,
reducing the number of pipeline creations helps to reduce execution time.

Affected tests:

   dEQP-VK.subgroups.*compute*

Components: Vulkan
VK-GL-CTS issue: 2019

Change-Id: Ie3ccbc53390bdba691c16d51c173b0a8a16119d9