Update git submodules

* Update docs/submodules/functest from branch 'master'
  - Merge "Remove $BRANCH in healthcheck/Dockerfile"
  - 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>

diff --git a/docs/submodules/functest b/docs/submodules/functest
index 171296a..551740e 160000 (submodule)
--- a/docs/submodules/functest
+++ b/docs/submodules/functest
@@ -1 +1 @@
-Subproject commit 171296aeab39e7274110856913fd21823a3a04cf
+Subproject commit 551740ee18dc83027654b9a0ef6de84901f86d84