Respect weight and country servers exclusions when selecting a country/city.

[ruihildt]

We would like to respect weight and country servers exclusions when selecting a country/city.

Here's what Linus had to say about it (He's probably the go to person if we have questions):

The roulette wheel selection algorithm to pick a relay from the filtered list:
https://github.com/mullvad/mullvadvpn-app/blob/master/mullvad-daemon/src/relays.rs#L632
11:20
And also referenced this: https://github.com/mullvad/mullvadvpn-app/blob/master/mullvad-daemon/src/relays.rs#L312
The algo has been updated today to support server with a weight of 0, see mullvad/mullvadvpn-app#3262