Code review comment for lp:~smoser/curtin/trunk.lp1716028-hack-file-locking-in-qemu

Note, i put this branch
 https://code.launchpad.net/~smoser/curtin/trunk.lp1716028-better-file-locking/
it has some code that i think is cleaner to turn --disk into -drive and -device
support, but I ended up shelving it because we couldn't use share-rw anyway
due to that not really working with -drive (see comments in bug).