Update git submodules

Update git submodules

* Update docs/submodules/releng from branch 'master'
  - Merge "[docs] local docs building for missing submodules"
  - [docs] local docs building for missing submodules

    Some projects already moved away from OPNFV Docs git submodules.
    The proposed hack has a couple of problems:
    - it still downloads all of OPNFV docs + submodules (recursively!);
    - it uses Jenkins to handle gerrit clone/fetch, just to nuke it and
      clone the current project again;
    But:
    - it is a small change, to be replaced when global-jjb will support
      gsutil upload for docs preview;
    - it provides a locally built preview document instead of the old
      (complete) doc preview;

    Change-Id: I7426679187eb1cfabb181c59da61f3b794e50e5f
    Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>