Update git submodules

Update git submodules

* Update docs/submodules/yardstick from branch 'stable/euphrates'
  - ping: always save rtt data, influxdb ignore empty data

    If the SLA was failing we were raising AssertionError and not storing
    the rtt in the data dict.  This caused influxdb parse errors because the
    data was empty.

    Fixup influxdb to ignore records with no data, so we don't try to parse
    no data.

    Change the ping logic to always record the rtt result even if the SLA
    was not met.

    Also fixup ping logic in cases where ping does not return results.  If
    SLA is defined use SLA * 10 otherwise use large float that doesn't break
    the grafana scale too much, maybe 999999

    JIRA: YARDSTICK-809

    Change-Id: Id2d51216581644a80e8c7b9aa98919a766008adf
    Signed-off-by: Ross Brattain <ross.b.brattain@intel.com>
    (cherry picked from commit af011b16787e8fd9fc6f918b1d1427dd1be562ec)