Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - collectd: set intel_pmu events path and OVS socket path

    switch from hardcoded path to dynamic path
    based on bin_path

    also enable proxy for install_collectd

    add barometer settings for virt and ovs_stats

    Change-Id: Id138aef548332a3e3fcb3963b746e7c9f10c0948
    Signed-off-by: Ross Brattain <ross.b.brattain@intel.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index a574265..6a904a3 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit a574265d16de75c904282b7ea0e2544b28a7996e
+Subproject commit 6a904a3a1b84e52861dcf4bf60332a666ae08b84