provide draft flag to build policy

Related: https://pagure.io/koji/issue/4014

builder/kojid

@@ -1123,6 +1123,7 @@ class BuildTask(BaseTaskHandler):
             'build_tag': build_tag,  # id
             'skip_tag': bool(self.opts.get('skip_tag')),
             'scratch': opts.get('scratch'),
+            'draft': opts.get('draft'),
             'from_scm': SCM.is_scm_url(src),
             'repo_id': opts.get('repo_id'),
         }

kojihub/kojihub.py

@@ -9863,7 +9863,7 @@ class IsDraftTest(koji.policy.BaseSimpleTest):
 
     def run(self, data):
         if 'draft' in data:
-            return data['draft']
+            return bool(data['draft'])
         if 'build' in data:
             build = get_build(data['build'])
             return build.get('draft', False)