This seems to miss the exit code of the dracut process, which actualy
caused some issues in I8511669e188717494daf2bc1384a6dd346f942a4 where
it would have been much clearer to stop after the initramfs generation
failed.
Add some debug messages, and catch any errors from the final call.
Change-Id: I6f89441ec4709f5199535e15a7cc53a3a8af273d