lib/random: unify random string generation into random.String

This was factored from fstest as we were including the testing
enviroment into the main binary because of it.

This was causing opening the browser to fail because of 8243ff8bc8.

vfs/test_vfs/test_vfs.go

@@ -18,6 +18,7 @@ import (
 	"time"
 
 	"github.com/rclone/rclone/lib/file"
+	"github.com/rclone/rclone/lib/random"
 )
 
 var (
@@ -35,24 +36,6 @@ func init() {
 
 }
 
-// RandomString create a random string for test purposes
-func RandomString(n int) string {
-	const (
-		vowel     = "aeiou"
-		consonant = "bcdfghjklmnpqrstvwxyz"
-		digit     = "0123456789"
-	)
-	pattern := []string{consonant, vowel, consonant, vowel, consonant, vowel, consonant, digit}
-	out := make([]byte, n)
-	p := 0
-	for i := range out {
-		source := pattern[p]
-		p = (p + 1) % len(pattern)
-		out[i] = source[rand.Intn(len(source))]
-	}
-	return string(out)
-}
-
 // Test contains stats about the running test which work for files or
 // directories
 type Test struct {
@@ -71,7 +54,7 @@ type Test struct {
 func NewTest(Dir string) *Test {
 	t := &Test{
 		dir:    Dir,
-		name:   RandomString(*nameLength),
+		name:   random.String(*nameLength),
 		isDir:  rand.Intn(2) == 0,
 		number: atomic.AddInt32(&testNumber, 1),
 		timer:  time.NewTimer(*timeout),
@@ -168,7 +151,7 @@ func (t *Test) rename() {
 		return
 	}
 	t.logf("rename")
-	NewName := RandomString(*nameLength)
+	NewName := random.String(*nameLength)
 	newPath := path.Join(t.dir, NewName)
 	err := os.Rename(t.path(), newPath)
 	if err != nil {