framework: sealert - provide a better error message when SELinux is disabled
    
    Fixes:
    $ sealert -a /var/log/audit/audit.log
    Opps, sealert hit an error!
    
    Traceback (most recent call last):
      File "/usr/bin/sealert", line 683, in <module>
        do_analyze_logfile(logfile)
      File "/usr/bin/sealert", line 526, in do_analyze_logfile
        audit2why.init()
    ValueError: You must specify the -p option with the path to the policy file.