Update git submodules

* Update docs/submodules/yardstick from branch 'stable/fraser'
  - Add ODL HA testcase

    This testcase confirms the resiliency of Opendaylight
    in a HA deployment

    SPEC: https://gerrit.opnfv.org/gerrit/#/c/50991

    JIRA: HA-33
    JIRA: YARSTICK-955

    Change-Id: I4cb39d1970ed0333a43fbb58f8c7138908379dcb
    Signed-off-by: Dimitrios Markou <mardim@intracom-telecom.com>
    (cherry picked from commit d16b2e14fe420a646d4399986bd9f4d1ae3a606d)

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index e00ef07..c778b24 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit e00ef072b2c0499061f3e375cbff0bc3f47fb35b
+Subproject commit c778b2494c4280035193a324a230b66ab9081300