Fix NoClassDefFoundException in BIRT tests on JDK7

java.lang.NoClassDefFoundError: org/eclipse/osgi/internal/loader/buddy/RegisteredPolicy
	at org.eclipse.osgi.internal.loader.buddy.PolicyHandler.getPolicyImplementation(PolicyHandler.java:67)
	...
        at org.eclipse.osgi.internal.baseadaptor.DefaultClassLoader.loadClass(DefaultClassLoader.java:107)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:356)
        ...
        at org.nuxeo.ecm.platform.reporting.api.BirtReportInstance.render(BirtReportInstance.java:163)
	at org.nuxeo.ecm.platform.reporting.tests.TestAdapters.testAdapters(TestAdapters.java:155)
        ...