Fix race condition in test 05-replicas-transfer.t

It's possible the compaction finishes before we're able
to monitor it.

Change-Id: I5b8fdeb0f9d3e0a7715a6b610622024e381a6450
Reviewed-on: http://review.couchbase.org/23606
Tested-by: Filipe David Borba Manana <fdmanana@gmail.com>
Reviewed-by: Filipe David Borba Manana <fdmanana@gmail.com>
Reviewed-on: http://review.couchbase.org/24662