lava_helper_configs.py: Fix regression test case pattern

Modify the test case pattern to match the new regression test output
string [1]

[1] https://tf.validation.linaro.org/scheduler/job/307975#L786

Signed-off-by: Arthur She <arthur.she@linaro.org>
Change-Id: Ie0b057293d34b152b187de0d50b98f9c343d0674
1 file changed