Update git submodules

* Update docs/submodules/functest from branch 'stable/euphrates'
  - Remove $BRANCH in healthcheck/Dockerfile

    This build arg is now useless because the multijobs call build.sh
    instead of the previous helper [1].

    [1] https://gerrit.opnfv.org/gerrit/#/c/47067/

    Change-Id: I52af9a5c4ed0775208d4467853f1b886a543de59
    Signed-off-by: Cédric Ollivier <cedric.ollivier@orange.com>
    (cherry picked from commit e045d841c8f52949088fbed007abd0c6df79d194)

diff --git a/docs/submodules/functest b/docs/submodules/functest
index 5d201d0..28c4803 160000 (submodule)
--- a/docs/submodules/functest
+++ b/docs/submodules/functest
@@ -1 +1 @@
-Subproject commit 5d201d0a539c1e3beeb72bbffd951636b1235087
+Subproject commit 28c4803587c071d9faef1abd0b444541d4b34b74