add err output when server failed to start

in same time than the port was opened.
Rename function into `wait_for_server` according.

src/server.rs

@@ -3,8 +3,7 @@ use mktemp::Temp;
 use std::io::{self, Cursor, Read};
 use std::process::{Child, ExitStatus, Stdio};
 use thiserror::Error;
-use zip::result::ZipError;
+use zip::{result::ZipError, ZipArchive};
-use zip::ZipArchive;
 
 #[derive(Debug, Error)]
 pub enum Error {
@@ -123,7 +122,7 @@ impl Drop for EmbeddedServer {
 mod utils {
     use super::Error;
     use std::fmt::Write;
-    use std::io::{BufRead, BufReader, ErrorKind};
+    use std::io::{BufRead, BufReader};
     use std::process::Child;
     use std::time::Duration;