iotests: Tweak 030 in order to trigger a race condition with parallel jobs

iotests: Tweak 030 in order to trigger a race condition with parallel jobs

This patch tweaks TestParallelOps in iotest 030 so it allocates data
in smaller regions (256KB/512KB instead of 512KB/1MB) and the
block-stream job in test_stream_commit() only needs to copy data that
is at the very end of the image.

This way when the block-stream job is awakened it will finish right
away without any chance of being stopped by block_job_sleep_ns(). This
triggers the bug that was fixed by 3d5d319e1221082974711af1d09d82f and
1a63a907507fbbcfaee3f622907ec24 and is therefore a more useful test
case for parallel block jobs.

After this patch the aforementiond bug can also be reproduced with the
test_stream_parallel() test case.

Since with this change the stream job in test_stream_commit() finishes
early, this patch introduces a similar test case where both jobs are
slowed down so they can actually run in parallel.

Signed-off-by: Alberto Garcia <berto@igalia.com>
Cc: John Snow <jsnow@redhat.com>
Message-id: 20180306130121.30243-1-berto@igalia.com
Signed-off-by: Max Reitz <mreitz@redhat.com>