MB-25243: Make xerrors optional for cbstats
MB-25243: Make xerrors optional for cbstats

Change-Id: Ifa69478a56132b145468432b76ac4e9851c401a0
Reviewed-on: http://review.couchbase.org/80922
Tested-by: Build Bot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>
Reviewed-by: Jim Walker <1cd02e31b43620d7c664e038ca42a060d61727b9@couchbase.com>

daverigby/kv_engine,daverigby/kv_engine,daverigby/kv_engine,daverigby/kv_engine