The test performs several rounds of write-read cycles with the following
configuration attributes in a <write-read> config node
rounds determines the number of rounds (default is 4)
size determines the number of bytes written/read in one round
(default is 4 MiB)
buffer_size determines the size of the write-read buffer
(default is 32 KiB)
In one round the test writes and reads "size/buffer_size" times
from/into a buffer_size'd buffer.
