Update git submodules

* Update docs/submodules/samplevnf from branch 'master'
  - Merge "Add support for multiple variables in core definition"
  - Add support for multiple variables in core definition

    In the [core] definition we were able to use one variable
    such as $core1 in [core $core1] but not [core ${core1}].
    The second syntax is used when we want multiple
    variables such as in [core ${first_core}-${last_core}].
    This second syntax is now supported.

    Change-Id: Ic94b84cb8cf827acb6697789cd180f41c3bdb028
    Signed-off-by: Xavier Simonart <xavier.simonart@intel.com>

diff --git a/docs/submodules/samplevnf b/docs/submodules/samplevnf
index 077f022..52919e3 160000 (submodule)
--- a/docs/submodules/samplevnf
+++ b/docs/submodules/samplevnf
@@ -1 +1 @@
-Subproject commit 077f0221942194640f8fa422580c62b27f938003
+Subproject commit 52919e307f83c2aa945e5d12c82fa4d7189529e8