test/py: efi_capsule: check the results in case of CAPSULE_AUTHENTICATE

Before the capsule authentication is supported, this test script works
correctly, but with the feature enabled, most tests will fail due to
unsigned capsules.
So check the results depending on CAPSULE_AUTHENTICATE or not.

Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
Reviewed-by: Simon Glass <sjg@chromium.org>