Update git submodules

Update git submodules

* Update docs/submodules/releng from branch 'master'
  to d77a45334371bcd8b0ddfa8b1062d5851a6670fc
  - Add tempest_slow in Functest gates

    It disables few ipv6 testcases due to possible SUT misconfigurations.
    It seems better than fully skipping ipv6 via tempest config [1]
    because it's already well covered in tempest_full.

    [1] https://docs.openstack.org/tempest/latest/sampleconf.html

    Change-Id: If1160dc68f5e53dffdfdd6722bdc557683243bde
    Signed-off-by: Cédric Ollivier <cedric.ollivier@orange.com>