Update git submodules

* Update docs/submodules/functest from branch 'stable/euphrates'
  - Clean Docker images after builds

    Compared to the related Releng script, it only focuses on cleaning
    images. It's considered out of scope to remove remaining docker
    containers.

    It doesn't force to remove images because base images (e.g. Alpine)
    could be selected by other OPNFV projects too. It ensures O is
    returned even if one image cannot be removed.

    functest-core is removed at the end because all Functest containers
    depend on it.

    The script works well in a nominal building env. Any remaining
    Functest images or containers must be removed by hand.

    Conflicts:
        build.sh

    JIRA: FUNCTEST-898

    Co-Authored-By: Cédric Ollivier <cedric.ollivier@orange.com>
    Change-Id: I72d8214b711680ec7958af1d427b23dee6337bf6
    Signed-off-by: Jose Lausuch <jalausuch@suse.com>
    Signed-off-by: Cédric Ollivier <cedric.ollivier@orange.com>
    (cherry picked from commit 98a942469134fcc3f91b6658a6fbb256d9d89518)

diff --git a/docs/submodules/functest b/docs/submodules/functest
index 8d28a82..f9e7142 160000 (submodule)
--- a/docs/submodules/functest
+++ b/docs/submodules/functest
@@ -1 +1 @@
-Subproject commit 8d28a8282aaf9aa738e7d43c2bf65ec0d4f20b6a
+Subproject commit f9e71426234fb0303b937d63cfa0020d4b24a267