Update git submodules

Update git submodules

* Update docs/submodules/releng-xci from branch 'master'
  - Merge "Simplify the serial config"
  - Simplify the serial config

    The current configuration only dumps the booting info into a file and
    the pty does not work (i.e. virsh console opnfv returns a failure
    because it cannot find a character device). After some investigations,
    it is apparently impossible to have both active:

    https://github.com/Mirantis/virtlet/issues/249

    Therefore, we should remove the pty part of the xml. To connect to the
    VM in case of network problems, we can always use vnc.

    Apart from that, the console part is not necessary as libvirt will
    create that one for us

    Change-Id: I80a59163b4ba4e6bff34cb5378893201e93ddb87
    Signed-off-by: Manuel Buil <mbuil@suse.com>