setup_repos: print the reason, if download failed

It happened a few times lately and I realized it's dumb that I
can't see why.

Signed-off-by: Adam Williamson <awilliam@redhat.com>

setup_repos.py

@@ -90,6 +90,7 @@ async def download_item(item, arch, targetdir):
         # "No .*available for {nvr}" indicates there are no
         # packages for this arch in the build
         if not f"available for {item}" in stderr:
+            print(f"Downloading {item} failed: {stderr}")
             return item
     return False