The simplest way is just add proxy=... entry to /etc/yum.conf, but sometimes it
is reasonable to bypass the proxy. Some examples:
- usage of non-standard repos with some exotic file layout, which will be
blocked by the proxy
- usage of repos not-accessible via proxy (eg only via VPN stared in VpnVM)
This commit introduces 'yum-proxy-setup' pseudo-service, which can be
controlled via standard qvm-service or qubes-manager. When enabled - yum will
be configured at VM startup to use qubes proxy, otherwise - to connect directly
(proxy setting will be cleared).
