Fix the length of the secret key.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-0.23@1389196 13f79535-47bb-0310-9956-ffa450edef68

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/security/token/SecretManager.java

@@ -81,7 +81,7 @@ public abstract class SecretManager<T extends TokenIdentifier> {
   /**
    * The length of the random keys to use.
    */
-  private static final int KEY_LENGTH = 20;
+  private static final int KEY_LENGTH = 64;
 
   /**
    * A thread local store for the Macs.