MB-8677 Ignore unindexable replicas on transfer set to active

Replicas on transfer look like normal active partitions
for the caller. Hence they can be marked as unindexable.
The actual transfer to a real active partition needs to
happen though. Thus an intersection between newly activated
partitions and unindexable ones is possible.

Change-Id: I8b36741f0d25f9a902a78c113c38d23042010d8e
Reviewed-on: http://review.couchbase.org/27803
Reviewed-by: Filipe David Borba Manana <fdmanana@gmail.com>
Tested-by: Filipe David Borba Manana <fdmanana@gmail.com>