HDFS-4982. JournalNode should relogin from keytab before fetching logs from other JNs. Contributed by Todd Lipcon.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1502682 13f79535-47bb-0310-9956-ffa450edef68
Merge remote-tracking branch upstream/$:{upbranch}