Investigate HDFS directory delete protection impacts (if any)

Was asked if enabling if HDFS directory write protections (added with https://issues.apache.org/jira/browse/HDFS-15243) would prevent Accumulo from cleaning up sub-directories.

This issue is to:

1) Determine if Accumulo deletes non-empty directories directly.
2) See if there is any impact if something like /accumulo/[instance_id]/tables was "delete" protected - could that be enabled without impacting Accumulo?
3) See if / what would need to be changed to allow this feature to be enabled in HDFS.

Start by tracing Accumulo's cleanup paths and reviewing the HDFS-15243 directory protection behavior. Check whether non-empty directories are deleted directly and whether protection on /accumulo/[instance_id]/tables affects cleanup. Done means documenting the impact and any changes required to enable the HDFS feature.

Written by the indexing model from the issue text.