Add github reporter status-url config option

Make it possible to set the github status link to something other than the
zuul server status_url. This allows the github status to link to the log output
for the jobs. If set, this url will be run through the same formatter
as the url_pattern used for comment links. If unset, it will fall back to the
previous behaviour of using the zuul server status_url.

Handle status-url from the reporter config and the zuul config the same
way and remove the hard coded change url format from zuul.conf. If a
user wants to specify the change id in the status url they should use
a template string in the same way as configuring a reporter.

Co-Authored-By: Jamie Lennox <jamielennox@gmail.com>
Change-Id: I5f2ff35bb38426ddcd7f65798b4f114256a54847
diff --git a/tests/fixtures/layouts/reporting-github.yaml b/tests/fixtures/layouts/reporting-github.yaml
index c939f39..8dd35b0 100644
--- a/tests/fixtures/layouts/reporting-github.yaml
+++ b/tests/fixtures/layouts/reporting-github.yaml
@@ -29,6 +29,7 @@
       github:
         comment: false
         status: 'success'
+        status-url: http://logs.example.com/{pipeline.name}/{change.project}/{change.number}/{change.patchset}/
     failure:
       github:
         comment: false