Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "Introduced default values and remove unnecessary ones from ansible code image build code."
  - Introduced default values and remove unnecessary ones from ansible code image build code.

    Change-Id: Id711d6fdacaddeafb8550290503d6cb6c814ea70
    Signed-off-by: Maciej Skrocki <maciej.skrocki@intel.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index a87c090..f7a3cef 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit a87c0902f957beaf93e62f3aeb48584caf871a27
+Subproject commit f7a3cef287979664d1812cdd4dd88276732ec8b8