Running multi-threaded vkcts in slang mode produces errors

[dzysk]

When I tried running vkcts multi-threaded in slang mode I see random failures in tests that pass when run serially. When I disable slang and run vkcts multi-threaded the errors do not occur.

The errors are all similar to: "ERROR: Got non-white pixels on sub-case 1"

The command I run is (for each thread I have a different test list and I increase the log file name and cache file name by one): deqp-vk.exe --deqp-archive-dir=. --deqp-caselist-file=parallel1.txt --deqp-log-images=disable --deqp-log-shader-sources=disable --deqp-log-flush=disable --deqp-log-filename=TestResults1.qpa --deqp-shadercache-filename=shadercache1.bin