Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "Reduce the log level if TRex client is no connected"
  - Reduce the log level if TRex client is no connected

    If the TRex client is no connected, the testcase will write an exception
    log that will be thrown to the CLI. There is no need to show the
    traceback in the CLI in this case.

    The log level is reduced to "error".

    JIRA: YARDSTICK-1059

    Change-Id: I22a52cedd6479f4cf692ba16a8415f7b8f574ab1
    Signed-off-by: Rodolfo Alonso Hernandez <rodolfo.alonso.hernandez@intel.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index 066a45e..e42e6b7 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit 066a45edd22be0fa7dec8986b850d672a86ad0a3
+Subproject commit e42e6b7ae99590c9590d1d4c9dfffe90e2677977