Filter out seqs for partitions which are not held by the view group

The seqs cache should store only the seqnos for the partitions which
are tracked by the current view group. Seqnos for other partitions can
be discarded.

Change-Id: Ie3d1539ad1c423fd883ce741546fa640850bf8ae
Reviewed-on: http://review.couchbase.org/40368
Reviewed-by: Volker Mische <volker.mische@gmail.com>
Reviewed-by: Sarath Lakshman <sarath@couchbase.com>
Tested-by: buildbot <build@couchbase.com>