Update git submodules

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>