Update git submodules

Update git submodules

* Update docs/submodules/releng from branch 'master'
  - Merge "prototypes: bifrost: Do not use tmpfs for dib builds"
  - prototypes: bifrost: Do not use tmpfs for dib builds

    Using tmpfs seems somewhat unstable. For example the following
    error is observed on openSUSE hosts

    ERROR: failed to umount the /tmp/dib_image.RJBbahUd tmpfs

    As such, we set the dib_notmpfs variable to 'true' which mimics what
    upstream OpenStack scripts are doing already in
    project-config:tools/build-image.sh

    Change-Id: If050ab70303b3556fc1880a956f0ba1505d62050
    Signed-off-by: Markos Chandras <mchandras@suse.de>