MB-9730 Add native index view group cleanup

Implementation of native utility for viewgroup cleanup.
Details of a viewgroup can be passed to couch_view_group_cleanup command
via stdin and it will perform cleanup of nodes belonging to partitions
specified by cleanup_bitmask. Purged count can be read back from stdout.

Change-Id: I1482500dca0406a528a7b66349701a49915b3c77
Reviewed-on: http://review.couchbase.org/30758
Reviewed-by: Filipe David Borba Manana <fdmanana@gmail.com>
Tested-by: Filipe David Borba Manana <fdmanana@gmail.com>