Update git submodules

Update git submodules

* Update docs/submodules/releng from branch 'master'
  - Merge "jjb: xci: bifrost-cleanup: Retry 'gsutil rm' on failures"
  - jjb: xci: bifrost-cleanup: Retry 'gsutil rm' on failures

    Sometimes 'gsutil rm' may fail for unknown reasons like the following
    one:

    [...]
    / [7/10 objects]  70% Done
    / [8/10 objects]  80% Done
    / [9/10 objects]  90% Done
    Operation completed over 10 objects.
    CommandException: 1 files/objects could not be removed.

    Try a few more times to remove the objects before giving up.

    Change-Id: I6905a806446dac41ddc43d4195514a5233480ccd
    Signed-off-by: Markos Chandras <mchandras@suse.de>