Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "Make security group configurable - dovetail"
  - Make security group configurable - dovetail

    Make sercurity group can be configured via the context.
    The format would be:
    context:
      name: demo
      image: yardstick-image
      flavor: yardstick-flavor
      user: ubuntu
      security_group:
        rules:
            - remote_ip_prefix: "0.0.0.0/0"
              protocol: "tcp"
              port_range_min: 1
              port_range_max: 65535
            - remote_ip_prefix: "0.0.0.0/0"
              protocol: "udp"
              port_range_min: 1
              port_range_max: 65535
            - remote_ip_prefix: "0.0.0.0/0"
              protocol: "icmp"

    JIRA: YARDSTICK-1360

    Change-Id: I00c45767ee2d70b790590e824599d5a4c274bced
    Signed-off-by: rexlee8776 <limingjiang@huawei.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index 5b23c7f..c20af2d 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit 5b23c7f12857ea6d47f184046010b467949303e6
+Subproject commit c20af2d971faf510cda48ef9be50ffb929e500e7