Configure zuul to trigger jobs on special comments

Configure zuul to retrigger check jobs when a comment with just
'recheck' in the comment text is left on a change. Retrigger approval
jobs when a comment with just 'reverify' in the comment text is left
on a change.

Change-Id: If3d21b31f19fc84211703b8cad05654e3da16c48

modules/openstack-ci-config/files/zuul/layout.yaml

@@ -3,6 +3,8 @@ queues:
     manager: IndependentQueueManager
     trigger:
       - event: patchset-created
+      - event: comment-added
+        comment_filter: (?i)^\s*recheck\.?\s*$
     success:
       verified: 1
     failure:
@@ -14,6 +16,8 @@ queues:
       - event: comment-added
         approval:
           - approved: 1
+      - event: comment-added
+        comment_filter: (?i)^\s*reverify\.?\s*$
     start:
       verified: 0
     success: