Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "Document for Fraser test case results"
  - Document for Fraser test case results

    JIRA: YARDSTICK-1132

    In B and C releases, Yardstick provides an overview of the results of test cases developed by Yardstick, executed on OPNFV community labs.

    This work has not been done for the D and E releases, although result analysis for Euphrates is available at (https://wiki.opnfv.org/display/yardstick/Euphrates+release+test+results+analysis). We plan to restart to provide a basic test case results analysis for Fraser and compare performance data with Euphrates.

    This JIRA ticket will be resolved into 3 commits: 1. Document for E release test case data; 2. Document for F release test case data; 3. Document for results analysis.

    Change-Id: I3c59851c8878ba37145e6ad6958272a62bad3f52
    Signed-off-by: JingLu5 <lvjing5@huawei.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index 370b703..b4bba7a 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit 370b703896656f6b6949de05b6c44c98a72eee46
+Subproject commit b4bba7a8d9d1e3379209d13a3272412e55f1dc74