Update git submodules

Update git submodules

* Update docs/submodules/fuel from branch 'master'
  - Merge "reclass: apt_mk_version: stable"
  - reclass: apt_mk_version: stable

    Although previous commit d1b6119 changed the first reference of
    apt-mk repos to 'stable' from 'nightly', it missed the cluster model.

    This fixes redeploys with `-f`, which fail due to conflicts between
    already installed 'stable' packages and 'nightly' ones.

    Fixes: d1b6119

    Change-Id: I854bac86feaaa61da0b68d158e270eec1ee0ccb7
    Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>