Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - cover: another 'db type could not be determined' workaround

    Change-Id: Ib94ff2dfc86725e5367908296b5160f9565442b8
    Signed-off-by: Ross Brattain <ross.b.brattain@intel.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index f143efd..c42d562 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit f143efd61c874ff6d8e18073d7f2f716abad9864
+Subproject commit c42d56297d22afb4245eae76c43fa762e14993ab