Solution: use fdisk when the system is live to delete the main partition (this just deletes it from the file table and doesn't actually damage the partition in any way) and recreate it - as long as it has the same starting block and ends past the previous ending block it'll be fine. After that you can reboot (or use partprobe/kpartx to get the kernel to re-read the partition table) and then resize2fs <disk>, which does an online resize. No downtime!
If this does not work for your situation we can have your vm rebuilt fresh after the upgrade just let us know if you need help reimaging.
