Update git submodules

Update git submodules

* Update docs/submodules/releng from branch 'master'
  - Merge "updated auto.yaml with 6.0.0 tagging and release-notes URL"
  - updated auto.yaml with 6.0.0 tagging and release-notes URL

    patch 2:
    fixed leading space issue

    patch 3:
    cherry-picked commits that were merged in master since initial
    stable/fraser branch; applied to Auto stable/fraser; submitted;
    used resulting new stable/fraser SHA1 as the SHA1 for
    Auto release 6.0.0 (3a957...); didn't change original
    stable/fraser SHA1 as Auto branch stable/fraser (5c811...);
    branches: https://gerrit.opnfv.org/gerrit/#/admin/projects/auto,branches
    changes: https://gerrit.opnfv.org/gerrit/#/q/project:auto

    Change-Id: I39c6acaeacc749b17489553e2af52e06902d2828
    Signed-off-by: Gerard Damm <gerard.damm@wipro.com>
    Signed-off-by: Trevor Bramwell <tbramwell@linuxfoundation.org>