MB-23999: Perform CAS check only if item being stored is alive

MB-23999: Perform CAS check only if item being stored is alive

If the existing document is expired, then storing another
deleted document with a CAS results in a ENOENT instead of
returning EEXISTS. The CAS check on an expired document is only
applicable if the incoming document is not in Deleted state

Change-Id: Ib6b78dd50236770a6be27a5fe341e321ef4eaec2
Reviewed-on: http://review.couchbase.org/77217
Reviewed-by: Dave Rigby <daver@couchbase.com>
Tested-by: Build Bot <build@couchbase.com>