Add very basic parallel test runner

[sjagoe]

Basic idea:

A test runner that will:

• Assume no interaction between tests
• Flatten all test suites into a single list of tests to be executed.
• Feed tests into a queue
• Create a multiprocessing process pool (or similar), each worker of which will act as a consumer of the queue of tests to be executed
• The test results are fed into a return queue, consumed by the master to construct the test result