t3504: do check for conflict marker after failed cherry-pick

t3504: do check for conflict marker after failed cherry-pick

The test with disabled rerere should make sure that the cherry-picked
result does not have the conflict replaced with a recorded resolution.

It attempts to do so by ensuring that the file content is _not_ equal
to some other file. That by itself is a very dubious check because just
about every random result of an incomplete cherry-pick would satisfy
the condition.

In this case, the intent was to check that the conflicting file does
_not_ contain the resolved content. But the check actually uses the
wrong reference file, but not the resolved content. Needless to say
that the non-equality is satisfied. And, on top of it, it uses a commit
that does not even touch the file that is checked.

Do check for the expected result, which is content from both sides of
the merge and merge conflicts. (The latter we check for just the
middle separator for brevity.)

As a side-effect, this also removes an incorrect use of test_must_fail.

Signed-off-by: Johannes Sixt <j6t@kdbg.org>
Signed-off-by: Denton Liu <liu.denton@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>