create and rename usernames validated by new func (#2381)

Signed-off-by: Kristoffer Dalby <kristoffer@tailscale.com>

hscontrol/db/users.go

@@ -24,7 +24,7 @@ func (hsdb *HSDatabase) CreateUser(user types.User) (*types.User, error) {
 // CreateUser creates a new User. Returns error if could not be created
 // or another user already exists.
 func CreateUser(tx *gorm.DB, user types.User) (*types.User, error) {
-	err := util.CheckForFQDNRules(user.Name)
+	err := util.ValidateUsername(user.Name)
 	if err != nil {
 		return nil, err
 	}
@@ -89,7 +89,7 @@ func RenameUser(tx *gorm.DB, uid types.UserID, newName string) error {
 	if err != nil {
 		return err
 	}
-	err = util.CheckForFQDNRules(newName)
+	err = util.ValidateUsername(newName)
 	if err != nil {
 		return err
 	}