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/posix-diskid-check.go

@@ -46,10 +46,6 @@ func (p *posixDiskIDCheck) Hostname() string {
 	return p.storage.Hostname()
 }
 
-func (p *posixDiskIDCheck) LastError() error {
-	return p.storage.LastError()
-}
-
 func (p *posixDiskIDCheck) Close() error {
 	return p.storage.Close()
 }