Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "Add API to update hosts info about SUT"
  - Add API to update hosts info about SUT

    JIRA: YARDSTICK-674

    For some SUT which use domain name as endpoint and AUTH_URL, yardstick
    restAPI should support to add "ip domain_name" info into /etc/hosts so
    that it can use the ip_address to access the SUT.

    api: /yardstick/env/action
    description: update hosts info for domain name
    method: POST

    parameters:
    {
        "action": "update_hosts",
        "args": {"opnfv.org": "1.1.1.1",
                 "openstack.org": "2.2.2.2"
                }
    }

    Change-Id: Iee1defaf069ebcb0328a37a659024eabac297482
    Signed-off-by: rexlee8776 <limingjiang@huawei.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index c532071..917dea4 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit c5320714338e4f819c329faaa618630382f3b68c
+Subproject commit 917dea49415183eaff6d2f2fbf32ddeff64d9dfe