t2400: avoid losing exit status to pipes

t2400: avoid losing exit status to pipes

The exit code of the preceding command in a pipe is disregarded. So
if that preceding command is a Git command that fails, the test would
not fail. Instead, by saving the output of that Git command to a file,
and removing the pipe, we make sure the test will fail if that Git
command fails.

Signed-off-by: Achu Luma <ach.lumap@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>