MB-7629 Add filter support for view compactor

A filter bitmask can be used to optionally ignore kvs
from certain vbuckets while rewriting the btrees to
the target index file during compaction.

Change-Id: I1e37834f062de10da29208a88619c5e3580f4de6
Reviewed-on: http://review.couchbase.org/31776
Reviewed-by: Filipe David Borba Manana <fdmanana@gmail.com>
Tested-by: Filipe David Borba Manana <fdmanana@gmail.com>