Update git submodules

* Update docs/submodules/releng from branch 'master'
  to 16ffbff2c72591d16e2baac12eadc3f66969d54d
  - Merge "Manage block_migration_for_live_migration"
  - Manage block_migration_for_live_migration

    It follows the change "Use block devices for live migration" in
    Functest [1]. It keep the value as False if ceph.

    [1] https://gerrit.opnfv.org/gerrit/#/c/67729/

    Change-Id: If4230344040815581805ce7268120994c4314ea2
    Signed-off-by: Cédric Ollivier <cedric.ollivier@orange.com>

diff --git a/docs/submodules/releng b/docs/submodules/releng
index af641dc..16ffbff 160000 (submodule)
--- a/docs/submodules/releng
+++ b/docs/submodules/releng
@@ -1 +1 @@
-Subproject commit af641dcc16b6d7970831658aecfa4d6cce7ee136
+Subproject commit 16ffbff2c72591d16e2baac12eadc3f66969d54d