Update git submodules

Update git submodules

* Update docs/submodules/qtip from branch 'master'
  - Use legacy storperf images instead of master branch

    The master branch of storperf is under refactoring and not stable
    enough for integration. It introduces microservices and some linked
    images is not built yet, e.g. storperf-graphite[1] which is required
    by storperf-master is empty

    [1] https://hub.docker.com/r/opnfv/storperf-graphite

    Change-Id: Ie8522dae9073d163872be5742a290fd003698442
    Signed-off-by: Yujun Zhang <zhang.yujunz@zte.com.cn>