Update git submodules

Update git submodules

* Update docs/submodules/oom/offline-installer.git from branch 'master'
  to cb3f68d8bcecb6ff55b223d16e7f91c871fb30b6
  - Decrease tests resource footprint on CI minion

    Due to constrained CI minion resources docker volumes
    need to be pruned after each test invocation to prevent
    false negative which occurs in case when multiple playbook
    level tests are run.

    Heavy VNC Server image (1GB) needs to be mocked with
    lightweight alpine image in play-infrastructure test
    for same reasons.

    Change-Id: I1026593a375853575cf210aefe29bc320d4e5c64
    Signed-off-by: Bartek Grzybowski <b.grzybowski@partner.samsung.com>
    Issue-ID: OOM-1907