Update git submodules

* Update docs/submodules/releng from branch 'master'
  - bugfix: container start failed due to config_file set to Nonetype

    Traceback (most recent call last):
      File "/usr/local/bin/opnfv-testapi", line 6, in <module>
        from opnfv_testapi.cmd.server import main
      File "/usr/local/lib/python2.7/dist-packages/opnfv_testapi/cmd/server.py", line 34, in <module>
        from opnfv_testapi.common.config import CONF
      File "/usr/local/lib/python2.7/dist-packages/opnfv_testapi/common/config.py", line 67, in <module>
        CONF = Config()
      File "/usr/local/lib/python2.7/dist-packages/opnfv_testapi/common/config.py", line 21, in __init__
        self._parse()
      File "/usr/local/lib/python2.7/dist-packages/opnfv_testapi/common/config.py", line 29, in _parse
        if not os.path.exists(self.config_file):
      File "/usr/lib/python2.7/genericpath.py", line 18, in exists
        os.stat(path)
    TypeError: coercing to Unicode: need string or buffer, NoneType found

    Change-Id: Ifa26b5b52e7f1c19a773b02ecc1c45b59b5dc09b
    Signed-off-by: SerenaFeng <feng.xiaowei@zte.com.cn>

diff --git a/docs/submodules/releng b/docs/submodules/releng
index 0c7bc1c..ab38b89 160000 (submodule)
--- a/docs/submodules/releng
+++ b/docs/submodules/releng
@@ -1 +1 @@
-Subproject commit 0c7bc1c58ce45b5c19a1c4f1a757363efe819a49
+Subproject commit ab38b8924b8b39eb44201f9bfa41f009a3eea0a1