framework: get_alert() to return level
    
    get_alert() returns an alert level
    
    level(s): "green", "yellow" or "red"
    
    Signature is now:
    get_alert(s: local_id) -> ssiasa(ssssbb)sss
    
    Fixes: https://github.com/fedora-selinux/setroubleshoot/issues/20