Update git submodules

Update git submodules

* Update docs/submodules/fuel from branch 'stable/euphrates'
  - Merge "salt.sh: Rework `git -C` for older git compat" into stable/euphrates
  - salt.sh: Rework `git -C` for older git compat

    CentOS 7.4 provides git 1.8.3, while `git -C` support was introduced
    in 1.8.5, so rework <salt.sh> to not rely on this parameter.

    Change-Id: Ied88466b2b3d91a3317922fa08f60afe934358a0
    Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>
    (cherry picked from commit 0adbe359a0e448e0a8007b0041890e33a612a4dc)