Use the qemu specific callback to fill this data in the qemu driver as
it's the only place where it was used and fix tests as the qemu test
capability object didn't configure the defaults for the tests.
This patch teaches testutil how to read multi-line input files with
backspace-newline line continuation markers.
The patch also breaks up all the single-line arguments test input files into
multi-line files with lines shorter than 80 characters.
