HADOOP-9352. Expose UGI.setLoginUser for tests (daryn)


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-0.23@1452340 13f79535-47bb-0310-9956-ffa450edef68
HDFS-4128. 2NN gets stuck in inconsistent state if edit log replay fails in the middle (kihwal via daryn)


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-0.23@1452391 13f79535-47bb-0310-9956-ffa450edef68
Merge remote branch 'origin/branch-0.23' into branch-0.23-gd
Merge remote branch 'origin/branch-0.23-gd' into fb-xxx-hadoop-auth-kerberos-realm-branch-0.23-gd