The result of TrueParallelTest is nondeterministic

The result of TrueParallelTest is inherently nondeterministic, on systems with high number of processors, the default number 5 of concurrent running threads is too low to make the test pass. On my 8 cores system, the test can rarely pass. This patch changes the number of threads to 4 times of available processors to make the test more likely to pass. But still the result of this test is nondeterministic. The patches can make the test less likely to fail.