Adding try/catch around close() call of the class loader

[xdevroey]

As suggested by @apanichella, I have added a try/catch statement around the close method call of the class loader to print an error message and continue the execution. The problem is related to a security policy of the JVM security manager, as indicated in the error messages:

Running the tests: [SBSTDummyForCoverageAndMutationCalculation, org.jsoup.parser.TokenQueue_ESTest]
Could not run the compiled tests!
java.util.concurrent.ExecutionException: java.lang.SecurityException: Security manager blocks ("java.lang.RuntimePermission" "closeClassLoader")
java.lang.Thread.getStackTrace(Thread.java:1559)
org.evosuite.runtime.sandbox.MSecurityManager.checkPermission(MSecurityManager.java:434)
java.net.URLClassLoader.close(URLClassLoader.java:290)
sbst.benchmark.coverage.TestExecutionTask.call(TestExecutionTask.java:65)
sbst.benchmark.coverage.TestExecutionTask.call(TestExecutionTask.java:17)
java.util.concurrent.FutureTask.run(FutureTask.java:266)
java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
java.lang.Thread.run(Thread.java:748)