MB-9730 Add support to stop cleaner native process

stop_cleaner() function needs to ensure that the
viewgroup cleanup native process has exited.
Added a mechanism to send exit message to native viewgroup
cleanup process and wait for process to exit and send exit status.

Change-Id: If187e2114a0608a8f704f6b43a3c36a4817035ab
Reviewed-on: http://review.couchbase.org/30988
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Filipe David Borba Manana <fdmanana@gmail.com>
Tested-by: Filipe David Borba Manana <fdmanana@gmail.com>