Update git submodules

* Update docs/submodules/bottlenecks from branch 'stable/danube'
  - Merge "Add description of environment clean-up" into stable/danube
  - Add description of environment clean-up

    JIRA: BOTTLENECK-165

    More details of the environment clean-up for ping test case

    Change-Id: I4b12a219155400235ae2bcb970efb3ba237153d9
    Signed-off-by: yuyang <Gabriel.yuyang@huawei.com>
    (cherry picked from commit 15355fd57080a7ac625549e9e9b98237164e46d2)

diff --git a/docs/submodules/bottlenecks b/docs/submodules/bottlenecks
index e6c4d13..6dff90f 160000 (submodule)
--- a/docs/submodules/bottlenecks
+++ b/docs/submodules/bottlenecks
@@ -1 +1 @@
-Subproject commit e6c4d136005fb214c676f8210337fc05f1f237ee
+Subproject commit 6dff90faee27dc5569255f5cb6ba72ae5e22b924