selftests/nolibc: add a standalone test report macro

The run-user, run and rerun targets use the same test report script,
let's add a standalone test report macro for them.

This shrinks code lines and simplify the future maintainability.

Suggested-by: Willy Tarreau <w@1wt.eu>
Link: https://lore.kernel.org/lkml/ZIB792FtG6ibOudp@1wt.eu/


Signed-off-by: Zhangjin Wu <falcon@tinylab.org>
Signed-off-by: Willy Tarreau <w@1wt.eu>