Update git submodules

* Update docs/submodules/sdnvpn from branch 'master'
  - Switch to Xtesting

    It inherits from xtesting.core.feature [1].

    [1] http://xtesting.readthedocs.io/en/latest/apidoc/xtesting.core.feature.html

    Change-Id: I3d64bce859de7132384b3cf0a6383348cc20b3b1
    Signed-off-by: Cédric Ollivier <cedric.ollivier@orange.com>

diff --git a/docs/submodules/sdnvpn b/docs/submodules/sdnvpn
index 6c768b6..349d25f 160000 (submodule)
--- a/docs/submodules/sdnvpn
+++ b/docs/submodules/sdnvpn
@@ -1 +1 @@
-Subproject commit 6c768b6740af8d537dc9735b7f36f0e8cc652511
+Subproject commit 349d25fb43e6a132edd80ce9c44a3982867eb0b7