Move all directory related functionality into paths utils

As per suggestion by @willscott in: https://github.com/OpenObservatory/gooni/pull/9#discussion_r176760264

utils/paths.go

@@ -0,0 +1,46 @@
+package utils
+
+import (
+	"errors"
+	"fmt"
+	"os"
+	"path/filepath"
+	"time"
+)
+
+// RequiredDirs returns the required ooni home directories
+func RequiredDirs(home string) []string {
+	requiredDirs := []string{}
+	requiredSubdirs := []string{"db", "msmts", "geoip"}
+	for _, d := range requiredSubdirs {
+		requiredDirs = append(requiredDirs, filepath.Join(home, d))
+	}
+	return requiredDirs
+}
+
+// GeoIPDir returns the geoip data dir for the given OONI Home
+func GeoIPDir(home string) string {
+	return filepath.Join(home, "geoip")
+}
+
+// DBDir returns the database dir for the given name
+func DBDir(home string, name string) string {
+	return filepath.Join(home, "db", fmt.Sprintf("%s.sqlite3", name))
+}
+
+// MakeResultsDir creates and returns a directory for the result
+func MakeResultsDir(home string, name string, ts time.Time) (string, error) {
+	p := filepath.Join(home, "msmts",
+		fmt.Sprintf("%s-%s", name, ts.Format(time.RFC3339Nano)))
+
+	// If the path already exists, this is a problem. It should not clash, because
+	// we are using nanosecond precision for the starttime.
+	if _, e := os.Stat(p); e == nil {
+		return "", errors.New("results path already exists")
+	}
+	err := os.MkdirAll(p, 0700)
+	if err != nil {
+		return "", err
+	}
+	return p, nil
+}