Maintenance: refactor servers updater code

- Require at least 80% of number of servers now to pass
- Each provider is in its own package with a common structure
- Unzip package with unzipper interface
- Openvpn package with extraction and download functions

internal/updater/providers/hidemyass/hosts.go

@@ -0,0 +1,19 @@
+package hidemyass
+
+func getUniqueHosts(tcpHostToURL, udpHostToURL map[string]string) (
+	hosts []string) {
+	uniqueHosts := make(map[string]struct{}, len(tcpHostToURL))
+	for host := range tcpHostToURL {
+		uniqueHosts[host] = struct{}{}
+	}
+	for host := range udpHostToURL {
+		uniqueHosts[host] = struct{}{}
+	}
+
+	hosts = make([]string, 0, len(uniqueHosts))
+	for host := range uniqueHosts {
+		hosts = append(hosts, host)
+	}
+
+	return hosts
+}