[FIX] runbot: avoid trying to push unexisting image

When an image is build for the first time and the build fails, an
ImageNotfound Exception is raised when trying to push the image.

Whith this commit, a warning is emmited instead of crashing in such a
case.

runbot/models/host.py

@@ -1,6 +1,7 @@
 import logging
 
 from collections import defaultdict
+from docker.errors import ImageNotFound
 
 from odoo import models, fields, api
 from odoo.tools import config, ormcache
@@ -145,7 +146,10 @@ class Host(models.Model):
             for dockerfile in self.env['runbot.dockerfile'].search([('to_build', '=', True)]):
                 dockerfile._build(self)
                 if is_registry:
+                    try:
                         docker_push(dockerfile.image_tag)
+                    except ImageNotFound:
+                        _logger.warning("Image tag `%s` not found. Skipping push", dockerfile.image_tag)
 
         _logger.info('Cleaning docker images...')
         for image in docker_images():