Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "Add UT: DurationRunner worker normal operation"
  - Add UT: DurationRunner worker normal operation

    * Use time.sleep to avoid multiprocessing.Queue broken pipe error.
    * Use a real duration in one of the test cases to test that the worker
      has successfully completed multiple iterations.

    JIRA: YARDSTICK-1199

    Change-Id: I0e14682d9993b69e2aa9fd9340a5a7620e9c0d8e
    Signed-off-by: Miikka Koistinen <miikka.koistinen@nokia.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index f0bf7df..50e5ba9 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit f0bf7dfe6c6eac91da27c72e2dc31166269f533b
+Subproject commit 50e5ba943e2959d79a77888199e2feae7ceb131a