Update git submodules

Update git submodules

* Update docs/submodules/functest from branch 'stable/euphrates'
  - Pull functest-core when only building childs

    Otherwise it fails if parent and childs containers are not built on
    the same host [1].

    It would have worked if the docker images were correctly cleant. Then
    the last image would have been pulled.

    [1] https://build.opnfv.org/ci/job/functest-apex-baremetal-daily-euphrates/362/console

    Conflicts:
        build.sh

    Change-Id: I293829c839c1cf68c9f7668aa643e16889359fcc
    Signed-off-by: Cédric Ollivier <cedric.ollivier@orange.com>
    (cherry picked from commit e3281b2175ca9983d79ce17de7e7497f749e650e)