[writeboost] Remove all WB(ERR|INFO|WARN) macros

As a device-mapper target, writeboost should follow the way other
targets do. To print out messages always with caller function's name helps
debugging in earlier stages but it is not helpful now. This patch
removes all WBXXX macros in writeboost target that does this. Instead
DMXXX macros overall.

Signed-off-by: Akira Hayakawa <ruby.wktk@gmail.com>
[writeboost] Remove the term "migrate"

Now we use two terms "writeback" and "migrate" to represent writing back
a block from cache to the backing device.
The term "writeback" is more intuitive so we don't use "migrate"
anymore.

Signed-off-by: Akira Hayakawa <ruby.wktk@gmail.com>
Merge pull request #19 from akiradeveloper/feature/remove-term-migrate

Feature/remove term migrate