Set default branch for repo

If, for some reason, a repo gets created via gerrit replication
instead of via the api, the default branch setting can be incorrectly
inferred. While we're setting things, just set master to be the default
branch everywhere.

Change-Id: I388afe670221bd8ec28fbba71041ab460e66411b

playbooks/roles/gitea-git-repos/tasks/setup-repo.yaml

@@ -45,3 +45,17 @@
       external_tracker_url: "https://storyboard.openstack.org/#!/project/{{ org }}/{{ repo }}"
       tracker_url_format: https://storyboard.openstack.org/#!/story/{index}
       tracker_issue_style: numeric
+- name: Set default branch
+  uri:
+    url: "{{ gitea_url }}/{{ org }}/{{ repo }}/settings/branches"
+    validate_certs: false
+    user: root
+    password: "{{ gitea_root_password }}"
+    force_basic_auth: true
+    status_code: 302
+    method: POST
+    body_format: form-urlencoded
+    body:
+      _csrf: "{{ gitea_token }}"
+      action: default_branch
+      branch: master