Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "Adopt infra_deploy to spawn VM on LTS Ubuntu 18"
  - Adopt infra_deploy to spawn VM on LTS Ubuntu 18

    Add possibility ro reuse infra_deploy.yaml to spawn VMs on jump host,
    depending on jump host Ubuntu version: either 16 or 18.

    JIRA: YARDSTICK-1396

    Change-Id: Id0682c03098e611fe3a51cbd24d8ff2dda7c552a
    Signed-off-by: Stepan Andrushko <stepanx.andrushko@intel.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index 7373f70..a8706c3 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit 7373f7063e234714fc14e1c59b1b24d018e632c0
+Subproject commit a8706c3b18f7f70798a0b20b1ec15ad496626784