Trace details of the replication events cancelled

When a destination is stopped, show in the replication_log
the number of pending and in-flight events cancelled.

The whole pending and in-flight cancellation is done through
a stateLock critical region, so that the state of the
destination object doesn't change in the middle of the
operation.

Change-Id: Ife2642bd4d1fd0ade627ace01b95bde6a9748d66