Update git submodules

Update git submodules

* Update docs/submodules/fuel from branch 'master'
  - Merge changes from topic 'docker-build'

    * changes:
      [docker build] Install OpenSSH server
      [submodule] Add docker-salt-formulas, ci/build.sh
      [deploy.sh] Install Docker if not present
      [jump req] Add build/deploy specific requirements

  - [docker build] Install OpenSSH server

    While at it, create the 'ubuntu' user with passwordless sudo
    and preinstall salt-formula-gnocchi (missing git repo workaround),
    as well as various useful packages (e.g. net-tools).

    JIRA: FUEL-383

    Change-Id: I5902c37110331acfd3fd4fccb92104de7b5ece6b
    Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>
  - [submodule] Add docker-salt-formulas, ci/build.sh

    - add new git submodule pointing to upstream docker build scripts;
    - add patch extending Docker tags with an '-(arch)' suffix,
      aligning with OPNFV tagging requiremnts;
    - add <ci/build.sh> wrapper for starting Docker builds;
    - install build-specific distro package requirements, as well as
      pip-managed packages (e.g. pipenv);

    JIRA: FUEL-383

    Change-Id: Id4fc886206d7eaf7e6d02810380f2391609ba405
    Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>
  - [deploy.sh] Install Docker if not present

    JIRA: FUEL-383

    Change-Id: I19d27ca59a3f24d1bd66e39457a6ca267bccce19
    Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>
  - [jump req] Add build/deploy specific requirements

    Add support for different prerequisites depending on the current
    operation (docker build or cluster deploy).

    Leverage the new support to pre-install upcoming deps:
    - python-pip (build);
    - docker-compose (deploy);

    JIRA: FUEL-383

    Change-Id: Ic3e6062b1943e3584f0b1f80d2e33b8812defced
    Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>