scanner: Return error to query if scannable snapshot is unavailable
scanner: Return error to query if scannable snapshot is unavailable

Change-Id: I1d1bf86fa583f48f26aef232cf8d0b8a8210b103
Reviewed-on: http://review.couchbase.org/43544
Reviewed-by: Deepkaran Salooja <94315e58ef7caa1d9829288fe30465d5fa6ccd83@gmail.com>
Reviewed-by: Sarath Lakshman <d41e430501c5d3aeeb2b91142f917f514040f807@couchbase.com>
Tested-by: Sarath Lakshman <d41e430501c5d3aeeb2b91142f917f514040f807@couchbase.com>

jchris/indexing,jchris/indexing,jchris/indexing,jchris/indexing