[writeboost] Remove term migrate

Now writeboost uses two terms "migrate" and "writeback" to
represent writeback. The term "writeback" is more intuitive so
we don't use the term "migrate" anymore.

This is a patch that must be merged atomically with
one to the kernel.

Signed-off-by: Akira Hayakawa <ruby.wktk@gmail.com>
Merge pull request #33 from akiradeveloper/feature/remove-term-migrate

[writeboost] Remove term migrate
[writeboost] Remove barrier_deadline_ms

In writeboost, Processing of write barriers is deferred.

Now there are two stages, 1) tunable deferment by timer which
queues a work and then 2) the work is dispatched.

This patch removes the first stage.

dm-thin and dm-cache do almost the same thing but they don't have such
complicated mechanism but only the second stage.
As a result of having the first stage, the code is complicated and hard
to understand, and also complicates the user interface.
I think of removing of this tunable for this reason.

Signed-off-by: Akira Hayakawa <ruby.wktk@gmail.com>
Merge pull request #34 from akiradeveloper/feature/remove-barrier-deadline-ms

[writeboost] Remove barrier_deadline_ms
[era] Check the kernel can understand restored metadata
Merge branch 'master' of github.com:jthornber/device-mapper-test-suite
[thinp-benchmarking] add an iozone benchmark
[thin benchmarking] update iozone tests
whitespace
[discard tests] some work in progress
[dm targets] start adding the raid target
update ignore file
thinp iozone test for snaps