Update git submodules

* Update plugins/replication from branch 'stable-2.16'
  to 6bff66dac4f9ad7e81d3e08d997285176d8edf8c
  - Fix NPE in PushResultProcessing
    
    The PushOne code passes a null to the notifier on cleanup when it
    encounters unknown states and this null gets passed all the way to
    PushResultProcessing which previously would NPE on it. Handle the null
    by outputting an "unknown" instead of crashing.
    
    Change-Id: I107d964a33349aaa5d6ae9aca68aab2889689155
    
  - Fix start --wait to track in-flight collisions and to not fail
    
    Previously when an in-flight collision occurred on a push that the
    'start --wait' command  was waiting for, the command would terminate
    with an error (and if it weren't for an NPE it would stop waiting
    prematurely). This was happening because PushOne is not tracking
    collisions resulting in its cleanup code assuming there was a failure.
    Fix this by tracking the collision in PushOne and skipping the cleanup
    in this case.
    
    Ironically, the NPE in change I107d964a33349aaa5d6ae9aca68aab2889689155
    was preventing the start command from receiving the premature
    termination on the collision, but it was not preventing the error. Thus
    this fix should get merged before fixing the NPE to avoid a worse
    scenario.
    
    Change-Id: Ibf1ca624739205f6f92e097213828faf29de9300
    Bug: Issue 12719
    
diff --git a/plugins/replication b/plugins/replication
index b7a86cd..6bff66d 160000
--- a/plugins/replication
+++ b/plugins/replication
@@ -1 +1 @@
-Subproject commit b7a86cdca9eac3c0cb4292202c04788bf000ea51
+Subproject commit 6bff66dac4f9ad7e81d3e08d997285176d8edf8c