Update git submodules

Update git submodules

* Update docs/submodules/releng-xci from branch 'master'
  - Bug fix: Remove use_prebuilt_images condition

    The creation or not of the IPA image does not depend on the value of the
    use_prebuilt_images. This variable is intended to control the following
    call to bifrost-create-dib-image role.

    I added a few comments to clarify what we are doing in each call to the
    bifrost-create-dib-image role

    Change-Id: Id66e1a969ca279a055640481719f118744eedf38
    Signed-off-by: Manuel Buil <mbuil@suse.com>