Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "Improve "Libvirt.virsh_create_vm" function"
  - Improve "Libvirt.virsh_create_vm" function

    Read the command exit code and raise an exception in case the VM boot
    process went wrong.

    JIRA: YARDSTICK-941

    Change-Id: Ibabaae8983213a33799ad00fa4d9541bbabea857
    Signed-off-by: Rodolfo Alonso Hernandez <rodolfo.alonso.hernandez@intel.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index 052a13a..79da68a 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit 052a13ab65063c2f50468161e278d348a403c660
+Subproject commit 79da68a8d4529bbc132228785f0e4c40506fa3ab