[sheepdog] [sheepdog/sheepdog] 6f7656: update MAINTAINERS

[Hitoshi Mitake]

  Branch: refs/heads/maintainers
  Home:   https://github.com/sheepdog/sheepdog
  Commit: 6f7656eaec4fe1aa89f3cebbad9c463e4e7ad22c
      https://github.com/sheepdog/sheepdog/commit/6f7656eaec4fe1aa89f3cebbad9c463e4e7ad22c
  Author: Hitoshi Mitake <mitake.hitoshi at gmail.com>
  Date:   2016-10-04 (Tue, 04 Oct 2016)

  Changed paths:
    M MAINTAINERS

  Log Message:
  -----------
  update MAINTAINERS

Update the maintainer lists of stable branch and OpenStack drivers.
This commit also removes obsolete stuff.

Signed-off-by: Hitoshi Mitake <mitake.hitoshi at lab.ntt.co.jp>