Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "model: pylint fixes"
  - model: pylint fixes

    remove redundnant parens
    replace type with isinstance
    fix import order

    Change-Id: I0407cbbf6993290f392f17c398827603b5bc1ebd
    Signed-off-by: Ross Brattain <ross.b.brattain@intel.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index c7114df..975860b 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit c7114df918ca1d463e49a1c41805e8f414100e7c
+Subproject commit 975860bd04dde49355c856449bcbf5cb290d7279