Exiting from a for-loop early using '|| break' does not propagate the
failure code, and for this reason, the tests used just 'exit'. But this
ends the test script with 'FATAL: Unexpected exit code 1' in the case of
a failed test.
Fix this by moving the loop into a shell function, from which we can
simply return early.
While at it, modernize the style of the affected test cases.
Signed-off-by: Johannes Sixt <j6t@kdbg.org> Signed-off-by: Junio C Hamano <gitster@pobox.com>