mojo reader: use stderr instead of stdout to show warnings

Description

Our application uses stdout to communicate predictions coming from mojos down to downstream processing.

Some models show warnings (see for example) on stdout.

Warnings are produced here -
https://github.com/h2oai/h2o-3/blob/8b9882de0701538be731a0b4110dbec8fb67bf09/h2o-genmodel/src/main/java/hex/genmodel/attributes/ModelJsonReader.java#L49

Stdout gets polluted by those warnings .

Please only use stderr for errors/ warnings.

Thanks.

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Assignee

Ruslan Dautkhanov

Fix versions

Reporter

Ruslan Dautkhanov

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