Update git submodules
Update git submodules

* Update plugins/replication from branch 'master'
  to 718d6210721cbfc38bbac6a3d976636fe17e4b72
  - Merge "Shard the waiting directory to scale better"
  - Shard the waiting directory to scale better
    
    Previously all the waiting tasks were stored in the same "waiting"
    directory. Since most filesystems don't scale well with more than 1000
    entries in a directory, shard the "waiting" directory by the first two
    characters of the taskKey. This will shard the waiting entries across a
    max of 256 subdirectories, potentially providing improved scalibility
    for up to 256K waiting entries.
    
    Change-Id: I4da79306cb75a868a30ed98d5b33432dc3656b19
    
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