Update git submodules

Update git submodules

* Update docs/submodules/releng from branch 'master'
  - Merge "jjb: xci: Use pre-built dib images for CI runs"
  - jjb: xci: Use pre-built dib images for CI runs

    We make use of the pre-built dib images hosted on artifacts.opnfv.org
    instead of building a new one on every CI build. This makes the CI jobs
    somewhat faster since we start with the XCI deployment straight away

    This patchset depends on https://gerrit.opnfv.org/gerrit/#/c/44049/

    Signed-off-by: Markos Chandras <mchandras@suse.de>
    Change-Id: Id2ccee8882cd20590a4cd27d4e512dc414d7b40e