iotests/030: Reduce job speed to make race less likely

It can happen that the throttling of the stream job doesn't make it slow
enough that we can be sure that it still exists when it is referenced
again. Just use a much smaller speed to make this very unlikely to
happen again.
Reported-by: NPeter Maydell <peter.maydell@linaro.org>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>
Message-Id: <20200716132829.20127-1-kwolf@redhat.com>
Reviewed-by: NMax Reitz <mreitz@redhat.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

tests/qemu-iotests/030

@@ -243,7 +243,7 @@ class TestParallelOps(iotests.QMPTestCase):
             node_name = 'node%d' % i
             job_id = 'stream-%s' % node_name
             pending_jobs.append(job_id)
-            result = self.vm.qmp('block-stream', device=node_name, job_id=job_id, base=self.imgs[i-2], speed=512*1024)
+            result = self.vm.qmp('block-stream', device=node_name, job_id=job_id, base=self.imgs[i-2], speed=1024)
             self.assert_qmp(result, 'return', {})
 
         for job in pending_jobs: