Suppress output of TestLoginWithoutTTY

Suppress the log line produced by `TestLoginWithoutTTY` in integration-cli suite:

```
+ go test -test.run TestLoginWithoutTTY -test.timeout=30m github.com/docker/docker/integration-cli
Username: time="2014-12-12T01:07:54Z" level="fatal" msg="inappropriate ioctl for device"
[PASSED]: login - login without TTY
```