Update git submodules

Update git submodules

* Update docs/submodules/releng-xci from branch 'master'
  - Merge "Download only necessary images for functest-smoke"
  - Download only necessary images for functest-smoke

    Functest download_images.sh script downloads images that are
    not needed for functest-smoke so we only download the necessary
    images to cut the time down.

    deploy-scenario:os-nosdn-nofeature
    installer-type:osa

    Change-Id: I0be643c4ccd4b8009e68433f5d635231afd2550a
    Signed-off-by: Fatih Degirmenci <fdegir@gmail.com>