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/unzip/extract.go

@@ -0,0 +1,36 @@
+package unzip
+
+import (
+	"archive/zip"
+	"bytes"
+	"io/ioutil"
+	"path/filepath"
+	"strings"
+)
+
+func zipExtractAll(zipBytes []byte) (contents map[string][]byte, err error) {
+	r, err := zip.NewReader(bytes.NewReader(zipBytes), int64(len(zipBytes)))
+	if err != nil {
+		return nil, err
+	}
+	contents = map[string][]byte{}
+	for _, zf := range r.File {
+		fileName := filepath.Base(zf.Name)
+		if !strings.HasSuffix(fileName, ".ovpn") {
+			continue
+		}
+		f, err := zf.Open()
+		if err != nil {
+			return nil, err
+		}
+		defer f.Close()
+		contents[fileName], err = ioutil.ReadAll(f)
+		if err != nil {
+			return nil, err
+		}
+		if err := f.Close(); err != nil {
+			return nil, err
+		}
+	}
+	return contents, nil
+}