Delay instantiation of DataSource as late as possible

Unfortunately it still has to happen in a @PostConstruct (otherwise
JPA never sees the schema in time), but we can delay a bit by not
using @Autowired. Appears to fix the Spring Cloud problem
(https://github.com/spring-cloud/spring-cloud-config/issues/105).

Fixes gh-2658

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/jdbc/DataSourceInitializer.java

@@ -50,7 +50,6 @@ class DataSourceInitializer implements ApplicationListener<DataSourceInitialized
 	@Autowired
 	private ConfigurableApplicationContext applicationContext;
 
-	@Autowired(required = false)
 	private DataSource dataSource;
 
 	@Autowired
@@ -59,11 +58,14 @@ class DataSourceInitializer implements ApplicationListener<DataSourceInitialized
 	private boolean initialized = false;
 
 	@PostConstruct
-	protected void initialize() {
+	public void init() {
 		if (!this.properties.isInitialize()) {
 			logger.debug("Initialization disabled (not running DDL scripts)");
 			return;
 		}
+		if (applicationContext.getBeanNamesForType(DataSource.class, false, false).length > 0) {
+			this.dataSource = applicationContext.getBean(DataSource.class);
+		}
 		if (this.dataSource == null) {
 			logger.debug("No DataSource found so not initializing");
 			return;