Bug 979299 - Reduce fragility in real time test. r=dburns, a=test-only

Sometimes the clock.sleep(0.1) may take shorter than 0.1 seconds.  This
isn't a test about precision in Python, but rather that the SystemClock
wrapper works as intended and returns a somewhat expected value.
Bug 981460 - Set download_block_table explicitly for testing applications. r=mmc, a=test-only