svn merge -c 1554815 merging from trunk to branch-2 to fix HADOOP-10173. Remove UGI from DIGEST-MD5 SASL server creation.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1554817 13f79535-47bb-0310-9956-ffa450edef68