Increase timeout in FatJarExporTests to avoid random test failures

Give it a max of 30s per test instead of 5s. This doesn't slow down the
tests execution, it just lets the tests run a bit longer if the hardware
is slow.

Fixes #699

org.eclipse.jdt.ui.tests/ui/org/eclipse/jdt/ui/tests/jarexport/FatJarExportTests.java

@@ -112,7 +112,7 @@ public class FatJarExportTests {
 	@Rule
 	public TestName tn=new TestName();
 
-	private static final int JAVA_RUN_TIMEOUT= 50; // 10th of a second
+	private static final int JAVA_RUN_TIMEOUT= 300; // 10th of a second
 
 	@BeforeClass
 	public static void setUpTest() {