SENTRY-432: Synchronization of HDFS permissions to Sentry permissions (Arun Suresh via Lenni Kuff)

This change adds support for synchronizing HDFS permissions with permissions stored in
Sentry. This makes it easy to share data across components (Hive/Impala, MR, Spark, etc)
while managing all privileges in a centralized location - Sentry. This is done using new
plugins to the HMS, HDFS, and Sentry. The HMS plugin pushes table/partition path information
to the Sentry Service, the Sentry Service forwards the path information and all privilege
updates, to the HDFS NameNode plugin, which caches this information and updates the ACLs
accordingly.

The mapping of Sentry privileges to HDFS privileges is:
ALL -> Read/Write access to data files
SELECT -> Read access to data files
INSERT -> Write access to data files