Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "Fix report generation"
  - Fix report generation

    The command "yardstick report generate task_id yaml_name" was returning
    some errors and failing to generate a html report.
    With this fix an html report will be generated with all data from influx.

    JIRA: YARDSTICK-1023

    Change-Id: If9aab4b85cfb2b5809f608568e1adb2ddeec8b78
    Signed-off-by: Xavier Simonart <xavier.simonart@intel.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index 8400c18..d9a19da 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit 8400c1895c49cb0c7802692f75d820fb5b8b7dc4
+Subproject commit d9a19da691a0cc258d26a2967983396b1c034b65