Add fallback trying of both known and new peers

[randomlogin]

Encountered on regtest. Probably not common for a live network as we hopefully can easily find a new peer.

Previously it was the following:

    pub(crate) fn select(&self) -> Option<Record> {
        if self.tried.is_empty() && self.new.is_empty() {
            return None;
        }
        let use_tried: bool = rand::random();
        if use_tried && !self.tried.is_empty() {
            return self.tried.select();
        }
        self.new.select()
    }

If tried.is_empty() = false and new.is_empty() = true we skip the first if, then we randomly choose use_tried = false then we skip the second if down to self.new.select() which fails as new.is_empty() = true.

Effectively this means if we cannot find a new peer there is a 50% chance we would not use the known ones and fail.

Not sure if we need a distinct test for that.

[rustaceanrob]

Please squash these into a single commit

[rustaceanrob]

Can we remove this test. I'm convinced this resolves the problem and further this is a regtest-only issue.

[rustaceanrob]

ACK e096884

Thanks