Update git submodules

Update git submodules

* Update docs/submodules/fuel from branch 'stable/euphrates'
  - [patch] system.repo: Add keyserver proxy support

    Instead of defining a http proxy for all salt-minion traffic, which
    also includes some Openstack API accesses we can't filter (no_proxy
    is not yet supported), add & leverage support for proxy configuration
    during APT keyserver access / key download.

    JIRA: FUEL-331

    Change-Id: I9470807633596c610cfafb141b139ddda2ff096b
    Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>
    (cherry picked from commit 6ab6935577900e598ca60aaed14d2e73f7b1633f)