Polish Elasticsearch health indicator

- Nest the configuration class in HealthIndicatorAutoConfiguration,
   bringing it into line with the other health indicator configuration
   classes
 - Include the statistics from the response in the health’s details
 - Map YELLOW to UP rather than UNKNOWN as it indicates that the cluster
   is running but that “the primary shard is allocated but replicas are
   not” [1]. The details can be used to determine the precise state of
   the cluster.
 - Add a property to configure the time that the health indicator will
   wait to receive a response from the cluster
 - Document the configuration properties
 - Update the tests to cover the updated functionality

See gh-2399

[1] http://www.elastic.co/guide/en/elasticsearch/reference/1.x/cluster-health.html

spring-boot-actuator/pom.xml

@@ -97,8 +97,8 @@
 			<optional>true</optional>
 		</dependency>
 		<dependency>
-			<groupId>org.springframework.data</groupId>
-			<artifactId>spring-data-elasticsearch</artifactId>
+			<groupId>org.elasticsearch</groupId>
+			<artifactId>elasticsearch</artifactId>
 			<optional>true</optional>
 		</dependency>
 		<dependency>
@@ -173,35 +173,40 @@
 			<optional>true</optional>
 		</dependency>
 		<!-- Test -->
+		<dependency>
+			<groupId>org.springframework.boot</groupId>
+			<artifactId>spring-boot</artifactId>
+			<type>test-jar</type>
+			<scope>test</scope>
+		</dependency>
 		<dependency>
 			<groupId>ch.qos.logback</groupId>
 			<artifactId>logback-classic</artifactId>
 			<scope>test</scope>
 		</dependency>
+		<dependency>
+			<groupId>org.apache.tomcat.embed</groupId>
+			<artifactId>tomcat-embed-logging-juli</artifactId>
+			<scope>test</scope>
+		</dependency>
 		<dependency>
 			<groupId>org.crashub</groupId>
 			<artifactId>crash.connectors.telnet</artifactId>
 			<scope>test</scope>
 		</dependency>
-		<dependency>
-			<groupId>org.springframework</groupId>
-			<artifactId>spring-test</artifactId>
-			<scope>test</scope>
-		</dependency>
 		<dependency>
 			<groupId>org.hsqldb</groupId>
 			<artifactId>hsqldb</artifactId>
 			<scope>test</scope>
 		</dependency>
 		<dependency>
-			<groupId>org.springframework.boot</groupId>
-			<artifactId>spring-boot</artifactId>
-			<type>test-jar</type>
+			<groupId>org.springframework</groupId>
+			<artifactId>spring-test</artifactId>
 			<scope>test</scope>
 		</dependency>
 		<dependency>
-			<groupId>org.apache.tomcat.embed</groupId>
-			<artifactId>tomcat-embed-logging-juli</artifactId>
+			<groupId>org.springframework.data</groupId>
+			<artifactId>spring-data-elasticsearch</artifactId>
 			<scope>test</scope>
 		</dependency>
 	</dependencies>