[writeboost] Generate the same tests for each type

dm-writeboost has type.
- type 0: only RAM buffer
- type 1: type 0 + persistent logging

The tests can be shared thus generate the same tests for both tests.

Design outline:
- The only difference in the stack classes is the table method which is
  passed to the dmsetup create.
- Stack class is a factory. Test class only depends on the functionality
  of creating a stack.

More tests will be added to WriteboostTests

Signed-off-by: Akira Hayakawa <ruby.wktk@gmail.com>