t6022, t6046: test expected behavior instead of testing a proxy for it

t6022, t6046: test expected behavior instead of testing a proxy for it

In t6022, we were testing for file being overwritten (or not) based on
an output message instead of checking for the file being overwritten.
Since we can check for the file being overwritten via mtime updates,
check that instead.

In t6046, we were largely checking for both the expected behavior and a
proxy for it, which is unnecessary.  The calls to test-tool also were a
bit cryptic.  Make them a little clearer.

Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>