Treat ATTEST_KEY keys as signing keys

An ATTEST_KEY key is still used for signing things in certs, so
include a self-signed cert in this case too. Similarly, key
usage in the cert should include signing.

Bug: 197096139
Test: VtsAidlKeyMintTargetTes
Change-Id: Icd7af0d1bdcf98155951eb469349a7924e373f9a
5 files changed