Very occasionally, the driver transition thread for the DSC race
condition unit test can be preempted before queuing the driver
transition. This leads to the transitions de-queuing in an unexpected
order, causing the test to fail. In order to close the race window, a
thread would have to set its event _after_ blocking on a pending
transition, which is impossible. So, rather than using events to
synchronize the different threads in this test case, use polling to
ensure the different transitions are queued in the appropriate order.
If the given condition is not met, call schedule() to give the other
threads a greater chance to run.
Change-Id: I05edfa9200ca7831926153f3ff0ec9dbbbab3fed
CRs-Fixed: 2378469
26ef417482