Add a regression test for sticky bit support of OIV ReverseXML processor

HDFS-10505 added a new feature OIV ReverseXML processor to generate a fsimage from a xml file. However, if the files/directories in it has sticky bit, ReverseXML processor can not recognize it due to HADOOP-13508.

It seems HADOOP-13508 is an incompatible change in Hadoop 3. Would it be reasonable to add an overloaded FsPermission constructor that uses RawParser so that it reads sticky bits correctly? Or is it reasonable to backport HADOOP-13508 to branch-2?