MB-25464: Do not exit cbstats if stats_perform fails
MB-25464: Do not exit cbstats if stats_perform fails

Exiting early will prevent cbstats collecting stats from other buckets
when running with `-a`.

Change-Id: I36641b06c5c22ea0add46b3bbe91332ec0fc498a
Reviewed-on: http://review.couchbase.org/81627
Well-Formed: Build Bot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>
Reviewed-by: James Harrison <5c25a7b3db09830813688775bfc8e6de736a230c@couchbase.com>
Tested-by: Build Bot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>
Reviewed-on: http://review.couchbase.org/82140
Reviewed-by: Jim Walker <1cd02e31b43620d7c664e038ca42a060d61727b9@couchbase.com>
Tested-by: Jim Walker <1cd02e31b43620d7c664e038ca42a060d61727b9@couchbase.com>

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