Move github reporting to checks API

This changes from the "status" API to the "checks" API, which puts
results on the "checks" tab on github.

This also puts a button to re-run failed tests, for which we need to
listen to the "check_run" event to handle.

Change-Id: I9cef46182f88f62daf5791594174a9af8c70a82f

zuul.d/pipelines.yaml

@@ -37,22 +37,25 @@
         - event: pull_request
           action: comment
           comment: (?i)^\s*recheck\s*$
+        - event: check_run
     start:
       github:
-        status: pending
+        check: 'in_progress'
         comment: false
     success:
       gerrit:
         # Note that gerrit keywords are case-sensitive.
         Verified: 1
       github:
-        status: 'success'
+        check: 'success'
+        comment: false
       mysql:
     failure:
       gerrit:
         Verified: -1
       github:
-        status: 'failure'
+        check: 'failure'
+        comment: false
       mysql:
 
 - pipeline:
@@ -386,17 +389,20 @@
         - event: pull_request
           action: comment
           comment: (?i)^\s*recheck\s*$
+        - event: check_run
     start:
       github:
-        status: pending
+        check: 'in_progress'
         comment: false
     success:
       github:
-        status: 'success'
+        check: 'success'
+        comment: false
       mysql:
     failure:
       github:
-        status: 'failure'
+        check: 'failure'
+        comment: false
       mysql:
     # Don't report merge-failures to github
     merge-failure: