Improve readability of shouldFirePendingOnlyToStoredUri test

Make the ReplicationIT.shouldFirePendingOnlyToStoredUri easier
to read and simplify the extraction of the replication tasks
associated to a change ref, as regex matching isn't required
and could be misleading when reading the test.

Change-Id: Ib493275872b56bc04cdcfb541b7cfa7ecfb1e058