The checker now have the possibility to have multiple backup servers
The config file now allows the syntax backup_url=url1, url2, url3, ...
This allows to have more than one server to contact in case of corrupted content.
Also, improve content integrity checker's test coverage by adding a test that verify if the content integrity checker can repair the files if the content is exclusively distributed among multiple servers.
Migrated from D37 (view on Phabricator)