Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "OpenStack deployment: delete RS or all VMs"
  - OpenStack deployment: delete RS or all VMs

    New parameter is added to shell script to delete data for VMs either from
    input file or all.
    Added disk images removal as per new input parameter.

    JIRA: YARDSTICK-1123

    Change-Id: I8d2cee4a3a7ad7147f4d59303bab656d80370221
    Signed-off-by: Stepan Andrushko <stepanx.andrushko@intel.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index fd142c3..fc7f814 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit fd142c3fa24d0df4696deaae7d936770c6593edd
+Subproject commit fc7f81481982966ab9260534d815cfda272b8d44