Several improvements to qemu support
- Honor hd_img and hd_size, if they're set.
- Change default hd_img format and extension to qcow2.
- Use -drive instead of -hda for more options and performance.
- If hd_img isn't an absolute path, store it in tmp/qemu.
See: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=963265
Edited by Vagrant Cascadian