tests logs contain confusing exceptions

[monperrus]

in test logs, there are exceptions such as

--java.lang.ClassNotFoundException: vvvvv
java.lang.Exception: Error Loading Engine: java.lang.ClassNotFoundException: vvvvv
	at fr.inria.coming.core.extensionpoints.PlugInLoader.loadPlugin(PlugInLoader.java:23)
	at fr.inria.coming.main.ComingMain.loadAnalyzersFromCommand(ComingMain.java:313)
	at fr.inria.coming.main.ComingMain.loadModelAnalyzers(ComingMain.java:301)
	at fr.inria.coming.main.ComingMain.createEngine(ComingMain.java:218)
	at fr.inria.coming.main.ComingMain.run(ComingMain.java:137)
	at fr.inria.coming.spoon.patterns.InstanceMiningTest.testMainModeArg(InstanceMiningTest.java:101)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)

However, they do not indicate a test failure and as such are quite confusing.

We should not have any exception in the console test logs (related to #test)