If the host supports kvm, use is. If this is not the case but the kqemu
module is loaded, run qemu with kqemu optimization. Otherwise fall-back to
pure usermode qemu.
Also create the root filesystem from within the virtual env, this way there
will be no nasty suprises w.r.t interactions with the host machine. This
is important when we test booting to LVM, LUKS, and mdraid.
Harald Hoyer