[writeboost Add benchmark to see randread deterioration

In GitExtract test, we can see Writeboost deteriorates reads.
To see how and why Writeboost does so we use fio to conduct a pure
benchmarking.

Signed-off-by: Akira Hayakawa <ruby.wktk@gmail.com>
Merge pull request #20 from akiradeveloper/feature/measure-read-deteriorate

[writeboost Add benchmark to see randread deterioration