Update git submodules

Update git submodules

* Update docs/submodules/releng-xci from branch 'master'
  - Merge "bifrost: destroy-env.sh: Clean dib images by default"
  - bifrost: destroy-env.sh: Clean dib images by default

    The destroy-env.sh script is meant to clean the entire environment
    including the dib images that were built in a previous run. However,
    this step was only executed if requested exclicitly leaving old
    artifacts behind. As such, lets switch the default value in order to
    remove these images as expected.

    Change-Id: If3b91a621df50931ef3d666737cbc3bbea5d34b9
    Signed-off-by: Markos Chandras <mchandras@suse.de>