Switch some deqp-runner testing to integration tests

To fix #15 (closed), I was bothered by how we were handling and testing timeouts and wanted to refactor that, but to do that I found myself really wanting to test the actual deqp-runner instead of a mock of some of the binary's behavior. So, switch the DeqpMock tests to be integration tests using the actual deqp-runner binary, where we have a mock deqp binary that we use to produce the deqp behavior we need.