Fixes for ZookeeperConfigServerBootstrapper inconsistencies.

Do not create a property source if CuratorFramework is null in ZookeeperConfigDataLoader.

Do not register CuratorFramework twice in CuratorFactory

Fixes gh-290

Author: spencergibb

spring-cloud-zookeeper-config/src/main/java/org/springframework/cloud/zookeeper/config/ZookeeperConfigDataLoader.java

@@ -43,6 +43,10 @@ public ZookeeperConfigDataLoader(Log log) {
 	public ConfigData load(ConfigDataLoaderContext context, ZookeeperConfigDataResource resource) {
 		try {
 			CuratorFramework curator = context.getBootstrapContext().get(CuratorFramework.class);
+			if (curator == null) {
+				// this can happen if certain conditions are met
+				return null;
+			}
 			ZookeeperPropertySource propertySource = new ZookeeperPropertySource(resource.getContext(),
 					curator);
 			List<ZookeeperPropertySource> propertySources = Collections.singletonList(propertySource);

spring-cloud-zookeeper-core/src/main/java/org/springframework/cloud/zookeeper/CuratorFactory.java

@@ -117,8 +117,10 @@ public static void registerCurator(BootstrapRegistry registery, UriComponents lo
 			BootstrapContext context = event.getBootstrapContext();
 			if (predicate.test(context)) {
 				CuratorFramework curatorFramework = context.get(CuratorFramework.class);
-				event.getApplicationContext().getBeanFactory().registerSingleton("configDataCuratorFramework",
-						curatorFramework);
+				if (!event.getApplicationContext().getBeanFactory().containsBean("configDataCuratorFramework")) {
+					event.getApplicationContext().getBeanFactory().registerSingleton("configDataCuratorFramework",
+							curatorFramework);
+				}
 			}
 		});