Update git submodules

* Update docs/submodules/opera from branch 'stable/danube'
  - Clean nfvo-driver-vnfm-juju docker

    nfvo-driver-vnfm-juju docker is unstable and currently
    using a personal docker repository to keep a working
    one. function docker_clean will only clean docker from
    openoint

    Change-Id: I90d5b98a10e44e900fe231e4b29925889536af41
    Signed-off-by: Harry Huang <huangxiangyu5@huawei.com>
    (cherry picked from commit 79219733ea099837d77bf851adde66f6e06c1b5e)

diff --git a/docs/submodules/opera b/docs/submodules/opera
index 5a9cd98..d972244 160000 (submodule)
--- a/docs/submodules/opera
+++ b/docs/submodules/opera
@@ -1 +1 @@
-Subproject commit 5a9cd98783bf7547cb56b3da84521315d3354f21
+Subproject commit d97224431caa5f1187137f8bd2818d2f5bbaa83e