Try to make the tests for the Cassandra sample more robust

Cassandra sometimes takes a long time when dropping the test keyspace.
This results in the test failing due to an exception being thrown.
This commit attempts to make the tests more robust by catching and
logging any exceptions thrown during server cleanup.

spring-boot-samples/spring-boot-sample-data-cassandra/src/test/java/sample/data/cassandra/OrderedCassandraTestExecutionListener.java

@@ -17,15 +17,30 @@
 package sample.data.cassandra;
 
 import org.cassandraunit.spring.CassandraUnitDependencyInjectionTestExecutionListener;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
 import org.springframework.core.Ordered;
 
 public class OrderedCassandraTestExecutionListener
 		extends CassandraUnitDependencyInjectionTestExecutionListener {
 
+	private static final Logger logger = LoggerFactory
+			.getLogger(OrderedCassandraTestExecutionListener.class);
+
 	@Override
 	public int getOrder() {
 		return Ordered.HIGHEST_PRECEDENCE;
 	}
 
+	@Override
+	protected void cleanServer() {
+		try {
+			super.cleanServer();
+		}
+		catch (Exception ex) {
+			logger.warn("Failure during server cleanup", ex);
+		}
+	}
+
 }