download: don't download signatures when --no-validate given

- show full path to failed download location

- change test to -f in case meta.tar.xz:templates has a blank line it
  won't attempt to sed a directory

Signed-off-by: Dwight Engen <dwight.engen@oracle.com>
Acked-by: Stéphane Graber <stgraber@ubuntu.com>