MB-7629 Implement view compactor incremental progress stats

When view compactor makes progress, a stats callback
is used to update the current progress of inserted kvs.
For every percentage progress, the compactor program sends
inserted count stats through stdout.

Change-Id: I550a8ed077e6dda78753f4a944d0bff36a624540
Reviewed-on: http://review.couchbase.org/32316
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Filipe David Borba Manana <fdmanana@gmail.com>
Tested-by: Filipe David Borba Manana <fdmanana@gmail.com>