tf_fuzz: fix sst `check ... except fail` calls

Fix the error code modelling of sst calls with data value checks (`check
...`), and except fail.

Currently, demo/8.test erroneously fails:

----
set sst name snortwaggle data *;
read sst name snortwaggle check "almost certainly not *this*" expect fail;
----

When reading `expect fail`, the sst read call is marked as "should
fail". However, the intended behaviour is for the read to succeed and
the check to fail.

To fix this, this patch adds a template variable, $check_expect, that
can be used to modify the expected value of the check (similar to how
$expect is used for expected values of calls). Using this, separate
pass/fail values can be set for the check as well as the call itself.

Change-Id: Ia55b6f2fef5737d67540e98ac6fc5e7695a8515f
Signed-off-by: Nik Dewally <Nik.Dewally@arm.com>
10 files changed