Update git submodules

* Update docs/submodules/releng from branch 'master'
  to c51c46c686895b20058c4de9fc961f1dcf14fba9
  - If releng verification has worked

    18:49:16 /usr/lib/python2.7/dist-packages/secretstorage/dhcrypto.py:15: CryptographyDeprecationWarning: Python 2 is no longer supported by the Python core team. Support for it is now deprecated in cryptography, and will be removed in the next release.
    18:49:16   from cryptography.utils import int_from_bytes
    18:49:16 DEPRECATION: Python 2.7 reached the end of its life on January 1st, 2020. Please upgrade your Python as Python 2.7 is no longer maintained. pip 21.0 will drop support for Python 2.7 in January 2021. More details about Python 2 support in pip can be found at https://pip.pypa.io/en/latest/development/release-process/#python-2-support pip 21.0 will remove support for this functionality.
    18:49:18 + python -m pip install --user --quiet --upgrade setuptools
    18:49:18 /usr/lib/python2.7/dist-packages/secretstorage/dhcrypto.py:15: CryptographyDeprecationWarning: Python 2 is no longer supported by the Python core team. Support for it is now deprecated in cryptography, and will be removed in the next release.
    18:49:18   from cryptography.utils import int_from_bytes
    18:49:18 DEPRECATION: Python 2.7 reached the end of its life on January 1st, 2020. Please upgrade your Python as Python 2.7 is no longer maintained. pip 21.0 will drop support for Python 2.7 in January 2021. More details about Python 2 support in pip can be found at https://pip.pypa.io/en/latest/development/release-process/#python-2-support pip 21.0 will remove support for this functionality.
    18:49:20 + python -m pip install --user --quiet --upgrade -r /tmp/requirements-EHaY.txt
    18:49:20 /usr/lib/python2.7/dist-packages/secretstorage/dhcrypto.py:15: CryptographyDeprecationWarning: Python 2 is no longer supported by the Python core team. Support for it is now deprecated in cryptography, and will be removed in the next release.
    18:49:20   from cryptography.utils import int_from_bytes
    18:49:20 DEPRECATION: Python 2.7 reached the end of its life on January 1st, 2020. Please upgrade your Python as Python 2.7 is no longer maintained. pip 21.0 will drop support for Python 2.7 in January 2021. More details about Python 2 support in pip can be found at https://pip.pypa.io/en/latest/development/release-process/#python-2-support pip 21.0 will remove support for this functionality.

    Change-Id: I936c36aa1ac694e3ac77e058ab6f13cccacee5eb
    Signed-off-by: Cédric Ollivier <cedric.ollivier@orange.com>

diff --git a/docs/submodules/releng b/docs/submodules/releng
index ca4ebaa..c51c46c 160000 (submodule)
--- a/docs/submodules/releng
+++ b/docs/submodules/releng
@@ -1 +1 @@
-Subproject commit ca4ebaa12ba7bb4ad1a364e1177b0d0498d706aa
+Subproject commit c51c46c686895b20058c4de9fc961f1dcf14fba9