[submodule] Add docker-salt-formulas, ci/build.sh

[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>