Update git submodules

* Update docs/submodules/samplevnf from branch 'stable/euphrates'
  - Merge "Adding index.rst for developer guide" into stable/euphrates
  - Adding index.rst for developer guide

    Change-Id: I642af0baf94501294b1d455d251c66f77e51757c
    Signed-off-by: Deepak S <deepak.s@linux.intel.com>

diff --git a/docs/submodules/samplevnf b/docs/submodules/samplevnf
index 6f2d777..9e89bb8 160000 (submodule)
--- a/docs/submodules/samplevnf
+++ b/docs/submodules/samplevnf
@@ -1 +1 @@
-Subproject commit 6f2d777637cc6a16200790a04080a8a22fd4b780
+Subproject commit 9e89bb88d02bb1235d8d120a49399daa9ad34347