download: Fix previous change

The previous change to support http proxies only worked when http_proxy
was set... Instead add some detection code and only use :80 when using
http_proxy.

That's a bit of a workaround, but it's the only way I could find to get
GPG to work with http_proxy.

Signed-off-by: Stéphane Graber <stgraber@ubuntu.com>
templates: Make sure usual locations are in PATH

Signed-off-by: Stéphane Graber <stgraber@ubuntu.com>
Acked-by: Serge E. Hallyn <serge.hallyn@ubuntu.com>