NCBC-192: Provide error constant for locate node failure

Change-Id: I70afd2fde695249c3b5dd21994b6d7cbe2d734d4
Reviewed-on: http://review.couchbase.org/23690
Reviewed-by: Matt Ingenthron <matt@couchbase.com>
Tested-by: John C. Zablocki <john@couchbase.com>