Update git submodules

* Update docs/submodules/releng from branch 'master'
  - Merge "[fuel] docker build: Add blocking jobs"
  - [fuel] docker build: Add blocking jobs

    Prevent master & stable streams to trigger concurrent builds on the
    same node, which usually leads to one of the jobs failing to acquire
    the DPDK lock on the build server.

    Change-Id: I1f61f1a2eb10eb9373a75b31c74f5d6de60f5334
    Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>

diff --git a/docs/submodules/releng b/docs/submodules/releng
index cd6690d..1974788 160000 (submodule)
--- a/docs/submodules/releng
+++ b/docs/submodules/releng
@@ -1 +1 @@
-Subproject commit cd6690d35f5152b0932e73fa15a8f3a4218ad42e
+Subproject commit 1974788bffc8469b9f05b5506e6e1e90fd2661a3