Update git submodules

Update git submodules

* Update docs/submodules/functest from branch 'stable/euphrates'
  - Merge "Allow building aarch64 images" into stable/euphrates
  - Allow building aarch64 images

    It must be noted that Docker automated build cannot create these
    images as the prerequisites are unmet to cross-compile [1].

    It also publishes a travis config file [2].

    [1] https://www.kernel.org/doc/html/v4.11/admin-guide/binfmt-misc.html
    [2] https://travis-ci.org/collivier/functest/builds/286932633

    Conflicts:
        build.sh

    Change-Id: I11fdef410cc40989132205a098410175f789fdef
    Signed-off-by: Cédric Ollivier <cedric.ollivier@orange.com>
    (cherry picked from commit ed777b643b05fbb71851df0b883483e0bcaa4ac1)