Add a health indicator for an Elasticsearch cluster

Closes gh-2399

spring-boot-actuator/pom.xml

@@ -96,6 +96,11 @@
 			<artifactId>spring-data-solr</artifactId>
 			<optional>true</optional>
 		</dependency>
+		<dependency>
+			<groupId>org.springframework.data</groupId>
+			<artifactId>spring-data-elasticsearch</artifactId>
+			<optional>true</optional>
+		</dependency>
 		<dependency>
 			<groupId>org.springframework.security</groupId>
 			<artifactId>spring-security-web</artifactId>