[SPARK-10349] [ML] OneVsRest use 'when ... otherwise' not UDF to generate new...

[SPARK-10349] [ML] OneVsRest use 'when ... otherwise' not UDF to generate new label at binary reduction

Currently OneVsRest use UDF to generate new binary label during training.
Considering that [SPARK-7321](https://issues.apache.org/jira/browse/SPARK-7321) has been merged, we can use ```when ... otherwise``` which will be more efficiency.

Author: Yanbo Liang <ybliang8@gmail.com>

Closes #8519 from yanboliang/spark-10349.