qemu: Add config for ./run --type qemu --test unittest

This allows the basic unittest config to be shared between

./run --type qemu --test unittest        and
./run --config qemu/cfg/unittests.cfg

While the latter may be the preferred invocation, I don't see any
reason to arbitrarily restrict things, especially when 'unittest'
shows up the --list-tests output.

Signed-off-by: Cole Robinson <crobinso@redhat.com>