Introduce new config parameter to download qcow2 image

Current http_image config format downloads tar.gz image which is no
more useful since recent changes in glance to fix CVE-2024-32498.
It will fail to import the image using web-download method as we
anticipate disk-format is qcow2 but it's not. Same it will further
fail if image_conversion plugin is enabled in the environment.

Introduced new config parameter http_qcow2_image which will by
default has reference to qcow2 image.

Change-Id: Ic07a55edc9a0ae713265220c9711f3dee48093fc
2 files changed