[writeboost] separate opts

Don't give opts more than one meaning.

Should be separated as
opts: option to stack
table_extra_args(new): option to table (k-v pairs)

Currently, these are mixed into opts only
and segregates the latter in making a table but this is confusing.

Signed-off-by: Akira Hayakawa <ruby.wktk@gmail.com>
[writeboost] add from_raw_status factory in WriteboostStatus

Signed-off-by: Akira Hayakawa <ruby.wktk@gmail.com>
[writeboost] Add rambuf_read_fullsize test

RAM buffer is really short-lived - it is soon flushed to cache device.
Thus, read-hit on RAM buffer is really unlikely in real-world system
which enables page cache to read in upper layer than block.

This test exploits PatternStomper to cover the RAM-buffer-read-hit case.
Also, WriteboostStatus is used to see if it really experienced the path.

Signed-off-by: Akira Hayakawa <ruby.wktk@gmail.com>
Merge pull request #17 from akiradeveloper/feature/add-rambuf-read-test

Feature/add rambuf read test