[mythtv] fixes to mythburn.py

[Stefan Brackertz]

>> Maybe we should alter mytharchive in a way that it runs
>> mythburn.py as a whole with ionice? Do you think that makes sense?
>
> Not if you want to actually burn the DVD from it.  Anyway, I've now
> fixed the calls for the tools that I use.  See the ticket for a combined
> patch.

Hm, what's the problem? I think growisofs uses the  
buffer-underrun-protection provided by all drives since 2004 by default.
Maybe one could test if the drive is able to protect underruns to be sure.

Stefan