Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - NSB: remove validate_cpu_cfg and all app cpu methods

    We don't really know what core we are going to use for the
    VNF before we generate the MultiPortConfig, so these
    methods are incorrect.

    We may need some more advanced method to validate
    the vCPU topology, but that will probably happen
    in the MultiPortConfig

    Change-Id: Ifee7ae4589ce0fce67771fb8d8b8dce0a0f06409
    Signed-off-by: Ross Brattain <ross.b.brattain@intel.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index 8291c3d..5a756e6 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit 8291c3d11227de42599be920605f3f884dfa755b
+Subproject commit 5a756e6171ad2d867914793dc2fd8b1aa7a19a6e