Start implementing new conduit stat summary endpoint.
Changes the public-api to call prometheus directly instead of the
telemetry service. Wired through to `api/stat` on the web server,
as well as `conduit statsummary` on the CLI. Works for deployments only.
Current implementation just retrieves requests and mesh/total pod count
(so latency stats are always 0).
Uses API defined in #663
Example queries the stat endpoint will eventually satisfy in #627
This branch includes commits from @klingerf
* run ./bin/dep ensure
* run ./bin/update-go-deps-shas
Risha Mars