Update git submodules

Update git submodules

* Update docs/submodules/functest from branch 'stable/fraser'
  - Bypass NoneType errors when creating router in rally

    It converts private subnet name to str as it's mandary till [1].
    It could be reverted as soon as [2] is merged in snaps.

    [1] https://gerrit.opnfv.org/gerrit/#/c/56091/
    [2] https://gerrit.opnfv.org/gerrit/#/c/56171/

    Change-Id: Ia728415207f8ecb5b5ac55982f82337c45671c4c
    Signed-off-by: Cédric Ollivier <cedric.ollivier@orange.com>
    (cherry picked from commit f0870e3735324941f5bd77243f36f9214cd531ac)