Polishing.

Align Oracle container versions for testing.

See #1179

spring-data-r2dbc/src/test/java/org/springframework/data/r2dbc/testing/ExternalDatabase.java

@@ -86,7 +86,7 @@ public abstract class ExternalDatabase implements BeforeAllCallback {
 
 		if (!checkValidity()) {
 			throw new TestAbortedException(
-					String.format("Cannot connect to %s:%d. Skipping tests.", getHostname(), getPort()));
+					String.format("Cannot connect to %s. Skipping tests.", this));
 		}
 	}
 

spring-data-r2dbc/src/test/java/org/springframework/data/r2dbc/testing/OracleTestSupport.java

@@ -125,12 +125,12 @@ public class OracleTestSupport {
 		if (testContainerDatabase == null) {
 
 			try {
-				OracleContainer container = new OracleContainer("springci/spring-data-oracle-xe-prebuild:18.4.0")
+				OracleContainer container = new OracleContainer("gvenzl/oracle-xe:18.4.0-slim")
 						.withReuse(true);
 				container.start();
 
 				testContainerDatabase = ProvidedDatabase.builder(container) //
-						.database("XEPDB1").build();
+						.database(container.getDatabaseName()).build();
 
 				DataSource dataSource = createDataSource(testContainerDatabase);