Stop creating redundant replication tasks from stream-events

Currently the broker-based ref-update triggers a replication
task once the event is received from the topic, even if the
apply-object was executed successfully beforehand.

To avoid this problem, an apply-objects cache has been introduced to
store temporally the apply-objects already successfully applied.

Bug: Issue 16885
Change-Id: Ib864bd0ae337f6b93308dfea155a22e1955409c3
12 files changed