Fix build regression from 08e5993a45c54926f8707e86b1ffad94b3e29a51

Signed-off-by: Rohit Yadav <rohit.yadav@shapeblue.com>
Revert "CLOUDSTACK-7959: fixed 'qemu-img convert' compat issue"

This reverts commit f412e07d715428b3b7d911e3cd0c71cd79949962.

Until we decide, we should keep the same 4.3 systemvm build scripts to avoid
changes in the qemu image conversion logic.
CHANGES: update changes file

Signed-off-by: Rohit Yadav <rohit.yadav@shapeblue.com>