KarafTestContainer.stop to also handle UncheckedIOException

[lichtin]

This section here should also catch UncheckedIOException

            if (shouldDeleteRuntime()) {
                system.clear();
                try {
                    FileUtils.forceDelete(targetFolder);
                }
                catch (IOException e) {
                    forceCleanup();
                }
            }

as can be seen by this stacktrace

java.io.UncheckedIOException: java.nio.file.NoSuchFileException: /jenkins/.../target/paxexam
	at org.apache.commons.io.function.Uncheck.wrap(Uncheck.java:242)
	at org.apache.commons.io.function.Uncheck.apply(Uncheck.java:164)
	at org.apache.commons.io.file.PathUtils.readAttributes(PathUtils.java:1259)
	at org.apache.commons.io.file.PathUtils.readPosixFileAttributes(PathUtils.java:1349)
	at org.apache.commons.io.file.PathUtils.deleteFile(PathUtils.java:582)
	at org.apache.commons.io.file.PathUtils.delete(PathUtils.java:476)
	at org.apache.commons.io.FileUtils.forceDelete(FileUtils.java:1337)
	at org.ops4j.pax.exam.karaf.container.internal.KarafTestContainer.stop(KarafTestContainer.java:707)
	at org.ops4j.pax.exam.spi.reactors.EagerSingleStagedReactor.tearDown(EagerSingleStagedReactor.java:118)
	at org.ops4j.pax.exam.spi.reactors.EagerSingleStagedReactor.afterClass(EagerSingleStagedReactor.java:132)
	at org.ops4j.pax.exam.spi.reactors.ReactorManager.afterClass(ReactorManager.java:441)
	at org.ops4j.pax.exam.junit.impl.ProbeRunner.run(ProbeRunner.java:107)
	at org.ops4j.pax.exam.junit.PaxExam.run(PaxExam.java:93)
	at org.apache.maven.surefire.junit4.JUnit4Provider.execute(JUnit4Provider.java:283)
	at org.apache.maven.surefire.junit4.JUnit4Provider.executeWithRerun(JUnit4Provider.java:173)
	at org.apache.maven.surefire.junit4.JUnit4Provider.executeTestSet(JUnit4Provider.java:153)
	at org.apache.maven.surefire.junit4.JUnit4Provider.invoke(JUnit4Provider.java:128)
	at org.apache.maven.surefire.booter.ForkedBooter.invokeProviderInSameClassLoader(ForkedBooter.java:203)
	at org.apache.maven.surefire.booter.ForkedBooter.runSuitesInProcess(ForkedBooter.java:155)
	at org.apache.maven.surefire.booter.ForkedBooter.main(ForkedBooter.java:103)