Add log4j logging for tests

[davsclaus]

We get this log4j warn when we run the tests

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 T E S T S
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Java HotSpot(TM) 64-Bit Server VM warning: ignoring option MaxPermSize=320m; support was removed in 8.0
Running org.apache.camel.idea.completion.extension.YamlPropertyPlaceholdersSmartCompletionTestIT
log4j:WARN No appenders could be found for logger (#com.intellij.util.ui.JBUI).
log4j:WARN Please initialize the log4j system properly.
log4j:WARN See http://logging.apache.org/log4j/1.2/faq.html#noconfig for more info.
Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 11.824 sec - in org.apache.camel.idea.completion.extension.YamlPropertyPlaceholdersSmartCompletionTestIT

We should add log4j logging and log to a test file / console etc so we can see a bit logging.