Update git submodules

* Update docs/submodules/yardstick from branch 'stable/fraser'
  - Merge "Convert SSH custom exceptions to Yardstick exceptions" into stable/fraser
  - Convert SSH custom exceptions to Yardstick exceptions

    JIRA: YARDSTICK-1215

    Change-Id: I5ecfd3dccd91b07cd8de5309dfa1a372eff16ed0
    Signed-off-by: Rodolfo Alonso Hernandez <rodolfo.alonso.hernandez@intel.com>
    (cherry picked from commit dde8fa628483deec352e176cea8decdbf6bed7e8)

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index 980ff9b..8cfd8dc 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit 980ff9b7b35bbb021c7d4cd2b9bc6a2a0b7eaa09
+Subproject commit 8cfd8dc7cba5719046f60139fca97b32841b902a