Wrong log severity in Dataflow logs

Hi, I'm not sure if this problem should be posted here, please correct me if it belongs to some GCP Dataflow specific issue tracker.

With a default logger configuration I see info logs as errors in GCP console.

Logger:
```

org.slf4j
slf4j-simple
1.7.25

```

Logging:
```

private Logger LOG = LoggerFactory.getLogger(MakeAlignmentViaHttpFn.class);
...
LOG.info(String.format("Sending
Alignment request (#%s) with %d elements...", ...));

```

Appears as "severity: ERROR" in GCP Console, see screenshot:

[https://user-images.githubusercontent.com/31351436/53070821-10e83f80-352c-11e9-93d2-bffeefaba6b8.png](https://user-images.githubusercontent.com/31351436/53070821-10e83f80-352c-11e9-93d2-bffeefaba6b8.png)

referring issue in my project: https://github.com/allenday/nanostream-dataflow/issues/58

Imported from Jira [BEAM-6930](https://issues.apache.org/jira/browse/BEAM-6930). Original Jira may contain additional context.
Reported by: bushkovsky.