[TC-534] Traffic Router statistics are not aggregated

[limited]

Looks like some of the stats APIs related to Traffic Router don't return proper data when there is more than 1 instance of Traffic Router (or will return data for OFFLINE TR).

This would affect statistics for Traffic Portal as an example.

Looking at the code, it doesn't seem to cycle through all the request routers available to get statistics from a Delivery Service as an example.

Known affected APIs :
/api/1.2/deliveryservices/:id/routing.json

Few things to take in consideration

• Skip OFFLINE traffic routers (I believe it does skip them today)
• Skip unreachable traffic routers
• Need to aggregate data? Numbers from `/api/1.2/deliveryservices/:id/routing.json` seems to be percentages. Does it matter to get an average from all request routers?

Note: I don't have full knowledge of what was intended by this API.

Author: Steve Malenfant
JIRA Link: https://issues.apache.org/jira/browse/TC-534
Found Version: 2.1.0