Identity: Fix breakage caused by recent changes in libsoft_attestation_cert.

CL:1566356 changed the notBefore and notAfter fields in the X.509
attestation certificate returned by generate_attestation_from_EVP().
This broke the default implementation of the Identity Credential HAL.

Fixed by setting TAG_CERTIFICATE_NOT_BEFORE and
TAG_CERTIFICATE_NOT_AFTER to the expected values.

Test: atest VtsHalIdentityTargetTest
Bug: 179933300
Change-Id: I2dbca41c1e905c17cd2bc565d2e987945b86273a