ZOOKEEPER-5021: Exit from zkCli when interrupt (Ctrl-C) or EOF (Ctrl-D) is pressed

Reviewers: ctubbsii, kezhuw
Author: PDavid
Closes #2369 from PDavid/ZOOKEEPER-5021-cli-fix-eof-interrupt-2

(cherry picked from commit 6c4fabf)
Signed-off-by: Andor Molnar <andor@cloudera.com>

Author: PDavid

zookeeper-server/src/main/java/org/apache/zookeeper/ZooKeeperMain.java

@@ -308,12 +308,13 @@ void run() throws IOException, InterruptedException {
         if (cl.getCommand() == null) {
             System.out.println("Welcome to ZooKeeper!");
 
-            boolean jlinemissing = false;
+            boolean jlinemissing = true;
             // only use jline if it's in the classpath
             try {
                 Class<?> readerC = Class.forName("org.jline.reader.LineReader");
                 Class<?> completerC = Class.forName("org.apache.zookeeper.JLineZNodeCompleter");
 
+                jlinemissing = false;
                 System.out.println("JLine support is enabled");
 
                 Object completer = completerC.getConstructor(ZooKeeper.class).newInstance(zk);
@@ -331,8 +332,9 @@ void run() throws IOException, InterruptedException {
                 | IllegalAccessException
                 | InstantiationException e
             ) {
-                LOG.debug("Unable to start jline", e);
-                jlinemissing = true;
+                if (jlinemissing) {
+                    LOG.debug("Unable to start jline", e);
+                }
             }
 
             if (jlinemissing) {