[further improvement] metric naming convention

[SidW]

Right now, Repository name, Sensor name, and Metric name are orthogonal. It makes more sense if prefixing the former in front of the latter and separating them by dot. That being said, if repository A has a sensor called B which contains metric C, the full name of this metric would be A.B.C.

Since JMX has the similar naming convention, this also makes it easier mapping metrics into corresponding JMX attribute.