SUSE dropped OpenStack Cloud in 2019 [1], and as a result, some
OpenStack-related repositories were removed from openSUSE Download and
root filesystem images stopped being provided. This change deprecates
Leap releases before 15.3 and employs the extract-image script. It also
moves the extract-image script to the sysprep element, since now it's
also used by openSUSE-related elements.
Additionally, revert the "Remove opensuse related funtests" change [2]
so that the opensuse element is tested again and set the default Leap
release to 15.3.
[1] https://www.zdnet.com/article/suse-drops-openstacks/
[2] https://review.opendev.org/c/openstack/diskimage-builder/+/824002
Change-Id: I73d6323aa65cee69a55e54bc53ed682f096dfc89
