Update the ModuleBuild.time_modified in case the `format_mmd` takes long time.
    
    In case there is lot of components in a module build or there are some
    networking issues and we need to retry the "git clone" commands, the
    `format_mmd` method can take long time.
    
    If it takes more than 10 minutes, the poller can produce fake event,
    because it seems the module build is stuck. This is wrong, because
    it would lead to another unexpected init handler call.
    
    In this commit, the `format_mmd` updates the `ModuleBuild.time_modified`
    method regularly to prevent poller from sending the unexpected fake
    init message.