shaarli: Backup/restore functional test timesout

When Shaarli is uninstalled and restored from a backup, the restore page never finishes loading after restore form submission. This is due to shaarli package restarting Apache during installation. This happens unnecessarily even when the required module (mod_rewrite) is already enabled. See bug #116936.

A workaround for the problem can be to make the backup and restore use Operation and show the progress. However, since restore involves installing apps (which are run as Operations), this would created nested Operations. We need to implement dealing with nested Operations.