HDFS-5383. fix broken caching unit tests (Andrew Wang)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/HDFS-4949@1533253 13f79535-47bb-0310-9956-ffa450edef68
HDFS-5203: finish plumbing through CacheManager#removeDescriptors
Merge branch 'HDFS-4949' into HDFS-5203
HDFS-5203: add new op to FSEditLogLoader