Fix buffer overflow in stats test

Change-Id: Ib5f6f50f894c28b8c7b7d646aa2428577dc8bebb
Reviewed-on: http://review.couchbase.org/44507
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>
Merge remote-tracking branch 'couchbase/master'

* couchbase/master:
  Fix buffer overflow in stats test

Change-Id: I8d836d387e00bbe3cd5c3514ea39bdce88cf3188