test/py: efi_secboot: add a test against certificate revocation

test/py: efi_secboot: add a test against certificate revocation

Revocation database (dbx) may have not only certificates, but also
message digests of certificates with revocation time
(EFI_CERT_X509_SHA256_GUILD).

In this test case, if the database has such a digest and if the value
matches to a certificate that created a given image's signature,
authentication should fail.

Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
Set defined time stamp for dbx_hash.auth.
Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>