Update git submodules

* Update docs/submodules/dovetail from branch 'master'
  - substitute image copy with docker volume

    Change-Id: Ie470d03bd168c909fd02c316523049c67a6bb095
    Signed-off-by: SerenaFeng <feng.xiaowei@zte.com.cn>

diff --git a/docs/submodules/dovetail b/docs/submodules/dovetail
index 3330fb6..6de223d 160000 (submodule)
--- a/docs/submodules/dovetail
+++ b/docs/submodules/dovetail
@@ -1 +1 @@
-Subproject commit 3330fb68a80794f8df503b2956a03f57613a601a
+Subproject commit 6de223dad312a4fac4a410fc4a4a21f457c06f27