Not all channels used for credential transport in systemd are trusted on SNP: while cmdline and initrd are measured and should be used, smbios and fwcfg are untrusted and the guest should ignore creds from those delivery paths. Implement an offensive credential test that tries to inject credentials via those untrusted channels and check the guest won't consume those credentials. Signed-off-by: Paul Meyer <katexochen0@gmail.com>