Fix images from live-respins-archive showing up in RespinRelease
Somebody decided it'd be a great idea to have this thing:
https://dl.fedoraproject.org/pub/alt/live-respins-archive/
which breaks our image finding because the basepath for
RespinRelease was alt/live-respins , and alt/live-respins-archive
matches that. We need to add a trailing slash to the basepath,
but then we need to tweak MirrorRelease.location too or else we
wind up with double slashes in the URLs. This all passes tests
so I'm, uh, totally sure it doesn't break anything else...
Signed-off-by: Adam Williamson <awilliam@redhat.com>