correct calculation of queue_time_secs; minor code formatting
correct calculation of queue_time_secs; minor code formatting

pauldardeau/python-concurrent-disk-io,pauldardeau/python-concurrent-disk-io,pauldardeau/python-concurrent-disk-io,pauldardeau/python-concurrent-disk-io,pauldardeau/python-concurrent-disk-io,pauldardeau/python-concurrent-disk-io,pauldardeau/python-concurrent-disk-io