The Open Build Service repository for the Leap 15.0 LXC image returns
a metalink which causes aria2c to download 2 files. The first is an
empty file (the metalink) and the second is the actual LXC image. The
name of the second file changes frequently.
This change uses the `--on-download-complete` callback of aria2c to
call a helper script which links the expected filename to the actual
filename.
Change-Id: I9a2bc7ded20f772af82956a81a9864c7ee17039c
Signed-off-by: Nicolas Bock <nicolas.bock@suse.com>