Since Ocata, backing images are by default converted into raw format
but since Pike a problem with O_DIRECT calls and ZFS backend storage
has presented - i.e., Pike on LXD with ZFS backend storage will result
in an error about image conversion. This config option allows
that default to be changed so that Pike on LXD with ZFS will lauch
instances succesfully.
Closes-Bug: 1710994
Change-Id: Ieba15b44b4b56a356d58c4504dd259fc80e7575d