HDFS-5925. ACL configuration flag must only reject ACL API calls, not ACLs present in fsimage or edits. Contributed by Chris Nauroth.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/HDFS-4685@1567450 13f79535-47bb-0310-9956-ffa450edef68