Update git submodules

* Update docs/submodules/releng from branch 'master'
  - Merge "Adding docker tag"
  - Adding docker tag

    Adds the tag to use when running docker from the DOCKER_TAG environment
    variable.

    Change-Id: I8f616b5582c1724079fec11c09f4cd3fdc72803f
    JIRA: STORPERF-128
    Signed-off-by: mbeierl <mark.beierl@dell.com>

diff --git a/docs/submodules/releng b/docs/submodules/releng
index a765f12..c08f0ef 160000 (submodule)
--- a/docs/submodules/releng
+++ b/docs/submodules/releng
@@ -1 +1 @@
-Subproject commit a765f12000378217a4b533525740bcceea3249d3
+Subproject commit c08f0ef55c70d61aa45c6268f2ab88bb4b446c28