Update git submodules

Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "Error in string format in HeatTemplateError message"
  - Error in string format in HeatTemplateError message

    There is a missing "s" in HeatTemplateError message [1].

    [1]https://github.com/opnfv/yardstick/blob/8400c1895c49cb0c7802692f75d820fb5b8b7dc4/yardstick/common/exceptions.py#L70

    JIRA: YARDSTICK-1047

    Change-Id: Ieb6fbf0af35d624015dbf34f34de7c7cc9145dd5
    Signed-off-by: Rodolfo Alonso Hernandez <rodolfo.alonso.hernandez@intel.com>