Update statistics of ACID tables during writes

When Impala INSERTs or TRUNCATEs an ACID table it simply removes the COLUMN_STATS_ACCURATE property to invalidate the statistics in order to prevent Hive using it.

Instead of it Impala should properly update the statistics. It should be relatively simple for TRUNCATE since it erases all the data, but a bit more complicated for INSERT, e.g.:

• Properly update number of distinct values
• INSERT OVERWRITE partition should properly update table level number of rows.