Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "Change assert statement to raise in common/utils"
  - Change assert statement to raise in common/utils

    This modification utilises a custom exception to be raised if an invalid
    mac address is passed to the function "mac_address_to_hex_list".

    JIRA: YARDSTICK-966

    Change-Id: Ic2940276f500e9710c54963a445a137e73bd6b25
    Signed-off-by: Miikka Koistinen <miikka.koistinen@nokia.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index 0258ce3..a844802 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit 0258ce3bc5713339cf0cf3d7e711cbd8d276f74f
+Subproject commit a84480299427f5380d6518069371de47346672c6