Add role path to JSON result in callback plugin

Having the role path is sometimes needed for debugging in case there are
multiple roles with the same name.

Change-Id: Icbd682a6cd84f2bcbaf07625f601316ffd2ea4fc

tests/remote/test_remote_zuul_json.py

@@ -94,6 +94,9 @@ class TestZuulJSON(AnsibleZuulTestCase):
             role_name = json_result[0]['plays'][0]['tasks'][0]['role']['name']
             self.assertEqual('json-role', role_name)
 
+            role_path = json_result[0]['plays'][0]['tasks'][0]['role']['path']
+            self.assertEqual('json-role', os.path.basename(role_path))
+
     def test_json_time_log(self):
         job = self._run_job('no-log')
         with self.jobLog(job):

zuul/ansible/callback/zuul_json.py

@@ -119,7 +119,8 @@ class CallbackModule(CallbackBase):
         if task._role:
             data['role'] = {
                 'name': task._role.get_name(),
-                'id': str(task._role._uuid)
+                'id': str(task._role._uuid),
+                'path': task._role._role_path,
             }
         return data