Update git submodules

Update git submodules

* Update docs/submodules/releng/builder from branch 'master'
  to e6600be8695cb9e21b47fabfc487d5b57a7f2420
  - Merge "Add a job to cleanup orphaned nodes"
  - Add a job to cleanup orphaned nodes

    This job assumes that releng minions have a 'prd' prefix and
    sandbox has a 'snd' prefix. These minions are Jenkins managed
    minions and are not Heat managed minions.

    The script get's a list of jobs with the prd or snd prefix and then
    checks against Jenkins to see if the nodes are attached to Jenkins
    if they are not then issue a delete call as it is likely Jenkins
    lost track of them.

    Issue: RELENG-724
    Change-Id: I624102ace279d49d2696d287cfea9e4e89ba7a20
    Signed-off-by: Thanh Ha <thanh.ha@linuxfoundation.org>