Informational messages are printed twice in 1.0.14

```
% gh-ost --database easypost --table rates --alter "MODIFY id BIGINT NOT NULL AUTO_INCREMENT" --allow-master-master
# Migrating `easypost`.`rates`; Ghost table is `easypost`.`_rates_gho`
# Migrating `easypost`.`rates`; Ghost table is `easypost`.`_rates_gho`
# Migrating db13sj:3306; inspecting db15sj:3306; executing on db15sj
# Migrating db13sj:3306; inspecting db15sj:3306; executing on db15sj
# Migration started at Mon Aug 29 23:58:19 +0000 2016
# Migration started at Mon Aug 29 23:58:19 +0000 2016
```

I initially thought that this was caused by `--concurrent-rowcount`, but it seems to happen regardless of `--concurrent-rowcount` with 1.0.14, and, in fact, it happens even with no special args, as shown above. Sometimes the messages are out-of-order, so I assume it's a race between two threads. Doesn't seem to affect actual execution.