Allow a null query.resultAlias in JmxTransConfiguraionXmlLoader

[andhan]

The ResultNameStrategyImpl#getResultName method has a default naming logic when query.getResultAlias() is null.

This default naming cannot currently be accessed when using the JmxTransConfigurationXmlLoader as this will create a query with an empty resultAlias rather than null when the resultAlias attribute is not set.

[cyrille-leclerc]

Thanks @andhan