HBASE-19581 Fixed remaining Checkstyle error in hbase-external-blockcache and enabled Checkstyle to fail on violations

hbase-external-blockcache/pom.xml

@@ -95,6 +95,22 @@
         <groupId>org.apache.maven.plugins</groupId>
         <artifactId>maven-source-plugin</artifactId>
       </plugin>
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-checkstyle-plugin</artifactId>
+        <executions>
+          <execution>
+            <id>checkstyle</id>
+            <phase>validate</phase>
+            <goals>
+              <goal>check</goal>
+            </goals>
+            <configuration>
+              <failOnViolation>true</failOnViolation>
+            </configuration>
+          </execution>
+        </executions>
+      </plugin>
     </plugins>
     <pluginManagement>
       <plugins>

hbase-external-blockcache/src/main/java/org/apache/hadoop/hbase/io/hfile/MemcachedBlockCache.java

@@ -1,4 +1,3 @@
-
 /**
  * Copyright The Apache Software Foundation
  *
@@ -29,6 +28,12 @@ import java.util.List;
 import java.util.NoSuchElementException;
 import java.util.concurrent.ExecutionException;
 
+import net.spy.memcached.CachedData;
+import net.spy.memcached.ConnectionFactoryBuilder;
+import net.spy.memcached.FailureMode;
+import net.spy.memcached.MemcachedClient;
+import net.spy.memcached.transcoders.Transcoder;
+
 import org.apache.hadoop.conf.Configuration;
 import org.apache.hadoop.hbase.HConstants;
 import org.apache.hadoop.hbase.io.hfile.Cacheable.MemoryType;
@@ -41,12 +46,6 @@ import org.apache.yetus.audience.InterfaceAudience;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
-import net.spy.memcached.CachedData;
-import net.spy.memcached.ConnectionFactoryBuilder;
-import net.spy.memcached.FailureMode;
-import net.spy.memcached.MemcachedClient;
-import net.spy.memcached.transcoders.Transcoder;
-
 /**
  * Class to store blocks into memcached.
  * This should only be used on a cluster of Memcached daemons that are tuned well and have a