Update git submodules

Update git submodules

* Update docs/submodules/releng-xci from branch 'master'
  - Merge "Reduce complexity when using bifrost roles"
  - Reduce complexity when using bifrost roles

    We are using two variables which have a similar scope:
    - create_image_via_dib
    - use_prebuilt_images

    We could use one of them and not both. create_image_via_dib is selected
    because it also exists in upstream bifrost

    use_prebuilt_images = false is the same as create_image_via_dib = true
    use_prebuilt_images = true is the same as create_image_via_dib = false

    Change-Id: Ieaab78f1dc2d199746a2b13ebc82e9dc615d92e9
    Signed-off-by: Manuel Buil <mbuil@suse.com>