Update git submodules

* Update docs/submodules/releng from branch 'master'
  - Merge "Support to build docker image with commit id"
  - Support to build docker image with commit id

    JIRA: DOVETAIL-447

    this support dovetail to make tag/container snapshot at some
    commit id

    this will also used for functest/yardstick if needed, since their danube.2.0/3.0
    may not satisfy dovetail requirements, while their snapshots at some commit id
    satisfy.

    Change-Id: I76cf6df586d1c9f0f563c6bfc039e3e271dc3de8
    Signed-off-by: MatthewLi <matthew.lijun@huawei.com>

diff --git a/docs/submodules/releng b/docs/submodules/releng
index 056b7cc..78ef942 160000 (submodule)
--- a/docs/submodules/releng
+++ b/docs/submodules/releng
@@ -1 +1 @@
-Subproject commit 056b7ccefe38b13e4b4eb11ff7e259e254e35c32
+Subproject commit 78ef9426c9f8dd97e4ea886b08eea593264aec9b