fix: avoid race condition by not running exec/start twice (#702)

ContainerExecAttach implicitly runs ContainerExecStart while attaching
to stdout/stderr.
Ref: e02bc91dcb/client/container_exec.go (L40)

Calling both can lead to a race condition as observed in #627

Fixes: #627

Co-authored-by: Markus Wolf <markus.wolf@new-work.se>

Co-authored-by: Markus Wolf <markus.wolf@new-work.se>

pkg/container/docker_run.go

@@ -456,13 +456,6 @@ func (cr *containerReference) exec(cmd []string, env map[string]string, user str
 			errWriter = os.Stderr
 		}
 
-		err = cr.cli.ContainerExecStart(ctx, idResp.ID, types.ExecStartCheck{
-			Tty: isTerminal,
-		})
-		if err != nil {
-			return errors.WithStack(err)
-		}
-
 		if !isTerminal || os.Getenv("NORAW") != "" {
 			_, err = stdcopy.StdCopy(outWriter, errWriter, resp.Reader)
 		} else {