[thin] Add a test to illustrate dct's over provisioning query
[writeboost] tweak the git extract test
Merge branch 'master' of github.com:jthornber/device-mapper-test-suite
[writeboost] Add Stack and Tests class to use backing device only for the same
tests as Writeboost

This patch also unwrap linear stacking from the backing device.
It doesn't need to use TVM to allocate backing device.

Signed-off-by: Akira Hayakawa <ruby.wktk@gmail.com>
Merge pull request #24 from akiradeveloper/feature/add-test-backing-only

[writeboost] Add Stack and Tests class to use backing device only for the same tests as Writeboost
[writeboost] Add dbench test

dbench can switch the SYNC frequency in the test by its option -S and -s.

- fix: measuring range in writeback-sorting test
- DEBUGMODE is added locally to test the tests (which is false by
  default). @param :: [] is added to each Tests class
- Stack#drop_caches added to cleanup the dirties in the SSD
  and apply this to other tests

Signed-off-by: Akira Hayakawa <ruby.wktk@gmail.com>