Update git submodules

Update git submodules

* Update cinder from branch 'master'
  to 616f134ba98adbd46277334b2d6361a522662f77
  - Merge "Doc: Improve docs for Glance Cinder Store"
  - Doc: Improve docs for Glance Cinder Store

    This patch improves the documentation for Cinder as a backend for
    Glance by including:
    1. Configuration changes with the New location API
    2. Details about how the optimizations are performed vs the generic path
    3. Pre-conditions for the optimizations to work
    4. Recommendations regarding the internal/service project while uploading volume

    Change-Id: I6f3035178b2b43145b34fbeb14bac22d0b52bc27
    Signed-off-by: Rajat Dhasmana <rajatdhasmana@gmail.com>