ZOOKEEPER-4906: Log full exception details for server JAAS config failure

Closes #2234

Signed-off-by: Zili Chen <tison@apache.org>
Signed-off-by: Andor Molnár <andor@apache.org>
Signed-off-by: Kezhu Wang <kezhuw@apache.org>

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

@@ -264,7 +264,7 @@ public abstract class ServerCnxnFactory {
                 if (loginContextName != null) {
                     errorMessage += " But " + ZooKeeperSaslServer.LOGIN_CONTEXT_NAME_KEY + " was set.";
                 }
-                LOG.error(errorMessage);
+                LOG.error(errorMessage, securityException);
                 throw new IOException(errorMessage);
             }
             return;