Update git submodules

* Update docs/submodules/releng from branch 'master'
  - nfvbench: Enable docker image builds for stable/euphrates

    Change-Id: I23ea156d9bbfa42c7bbf8dada344ded96b41e2e4
    Signed-off-by: Fatih Degirmenci <fatih.degirmenci@ericsson.com>

diff --git a/docs/submodules/releng b/docs/submodules/releng
index af0996b..be1c21b 160000 (submodule)
--- a/docs/submodules/releng
+++ b/docs/submodules/releng
@@ -1 +1 @@
-Subproject commit af0996b10798f9b648c098d3afc5c3d999b7e235
+Subproject commit be1c21bcd0b841b367de3348fcd84f5872652a1b