Implement a blocking version of a command to compact

currently

alter table AcidTable compact 'major'

is supported which enqueues a msg to compact.

Would be nice for testing and script building to support

 
alter table AcidTable compact 'major' blocking

perhaps another variation is to block until either compaction is done or until cleaning is finished.

DDLTask.compact() gets a request id back so it can then just block and wait for it using some new API

may also be useful to let users compact all partitions but only if a separate queue has been set up for compaction jobs.
The later is because with a 1M partition table, this may create very many jobs and saturate the cluster.
This probably requires HIVE-12376 to make sure the compaction queue does the throttling, not the number of worker threads