Use a colon instead of an underscore for the upragg stats seperator

Change-Id: Ia845cc7fa8a213fa6bb64faadeb6978bb12f5525
Reviewed-on: http://review.couchbase.org/37289
Reviewed-by: Sriram Ganesan <sriram@couchbase.com>
Reviewed-by: Chiyoung Seo <chiyoung@couchbase.com>
Reviewed-by: Sundararaman Sridharan <sundar@couchbase.com>
Tested-by: Sundararaman Sridharan <sundar@couchbase.com>