rest/storage: Remove racy LastError usage (#8817)

instead perform a liveness check call to
verify if server is online and print relevant
errors.

Also introduce a StorageErr string error type
instead of errors.New() deprecate usage of
VerifyFileError, DeleteFileError for gob,
change in datastructure also requires bump in
storage REST version to v13.

Fixes #8811

cmd/naughty-disk_test.go

@@ -57,10 +57,6 @@ func (*naughtyDisk) Hostname() string {
 	return ""
 }
 
-func (d *naughtyDisk) LastError() (err error) {
-	return nil
-}
-
 func (d *naughtyDisk) Close() (err error) {
 	if err = d.calcError(); err != nil {
 		return err