[IMP] runbot: update repo in reversed order

When updating repo, order is  odoo/odoo, odoo-dev/odoo, odoo/enterprise, odoo-dev/enterprise
The problem with this is that if a community hash and an enterprise hash arrives exactly
between odoo/odoo and odoo/enterprise update, enterprise could have a newest version
than community when creating builds.

By inversing this order, we have less chances to have this cornercase (as unlikelly as
it could be)

runbot/models/repo.py

@@ -344,7 +344,7 @@ class runbot_repo(models.Model):
     @api.multi
     def _update(self, force=True):
         """ Update the physical git reposotories on FS"""
-        for repo in self:
+        for repo in reversed(self):
             try:
                 repo._update_git(force)
             except Exception: