--test-on-replica should not write to binlogs

In our environment, we do not use GTID's and we run most clusters in an Active/Passive Master/Master configuration. The current behavior of gh-ost's test on replica function is that it assumes the host is a leaf node with no replicas and still writes the changes to the binlog.

It would be beneficial if there was an additional flag to not write to the binlog.

The specific situation I am in is that I am compressing some large tables. Based on small tests and estimates, we should have enough space to complete the compression of one table without running out of disk space. I had intended on running the migration on the passive master, which is taking no traffic and could run out of disk space without any negative issues. With the migration being written to the binlogs, though, this would also cause the active master to run out of space as well.