Bug#977721: Opening a block device as a file using the 'file' driver is deprecated

[Michael Tokarev]

Marc, are you using spice and audio, and have no qemu-user-gui package 
installed?
If yes, please try the same qemu usage but with qemu-user-gui package 
installed, --
it might be #977301 and the prob is due to qemu segfaulting due to unexpectedly
missing audio backend.

Thanks,

/mjt