Update git submodules

* Update docs/submodules/samplevnf from branch 'stable/euphrates'
  - Adjusted referencing for docs

    Change-Id: If9e92a2404214e91c682793622f097e28c11597d
    Signed-off-by: Sofia Wallin <sofia.wallin@ericsson.com>

diff --git a/docs/submodules/samplevnf b/docs/submodules/samplevnf
index 1482bf9..af6b181 160000 (submodule)
--- a/docs/submodules/samplevnf
+++ b/docs/submodules/samplevnf
@@ -1 +1 @@
-Subproject commit 1482bf952151f8ff1089547520f0844ff6f60768
+Subproject commit af6b18166ddbe9331c529256cb71c11e8b280982