Update git submodules

* Update docs/submodules/yardstick from branch 'stable/fraser'
  - NSB setup inventory name changed

    NSB setup script [1] fails when retrieving the inventory file. This script
    is going to be deprecated but we still support it.

    [1] https://github.com/opnfv/yardstick/blob/master/nsb_setup.sh

    JIRA: YARDSTICK-1247

    Change-Id: I3798531652b0e3a1a007d1d9434998fdd54645d7
    Signed-off-by: Rodolfo Alonso Hernandez <rodolfo.alonso.hernandez@intel.com>
    Signed-off-by: Mytnyk, Volodymyr <volodymyrx.mytnyk@intel.com>
    (cherry picked from commit 370b703896656f6b6949de05b6c44c98a72eee46)

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index f16b273..2ab8157 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit f16b2735436df989dabc01119217ae705b3913f3
+Subproject commit 2ab8157726c651c44be4d2f3ba54157ce778a536