MB-7629 Fix view compactor stopper to stop native process

Compactor stopper has to send a stop message to the
native compactor process and it has to die gracefully.
It should be waiting for native process to die after
sending stop message.

Change-Id: I07c02bd5585538b51e05e9d59595f5b684d8cc3c
Reviewed-on: http://review.couchbase.org/32310
Reviewed-by: Filipe David Borba Manana <fdmanana@gmail.com>
Tested-by: Filipe David Borba Manana <fdmanana@gmail.com>