Geo: set-geo-primary-node should be explicitly successful

The first step of setting up Geo is running gitlab-ctl set-geo-primary-node. The output doesn't explicitly state if it is successful:

Saving primary GeoNode with URL https://primary.example.com/

Original output

Saving primary GeoNode with URL http://primary/ 2017-04-14T16:39:40.951Z 4553 TID-ouaakc1zs INFO: Cron Jobs - add job with name: geo_bulk_notify_worker

This is, in fact, a success message, but it wasn't clear that it was.

Proposal

The goal of this command is to set the current node as the primary. Upon success, we should say

Saving primary geo node with URL https://primary.example.com/ ...
https://primary.example.com/ is now the primary geo node