test-e2e: update libvirt test case to support kbs with ibmse verifier.

[liudalibj]

In this issue we enhance the kbs related codes to support run test case on KBS with ibmse verifier
depend on confidential-containers/trustee#436

The deploy and test base on env IBM_SE_CREDS_DIR refer to https://github.com/confidential-containers/trustee/tree/main/kbs/config/kubernetes#deploy-kbs
All files in the folder IBM_SE_CREDS_DIR will be prepared by hand before we run the test case:

export IBM_SE_CREDS_DIR=/path/to/your/directory
tree $IBM_SE_CREDS_DIR
/path/to/your/directory#
.
├── certs
│   ├── ibm-z-host-key-signing-gen2.crt
|   └── DigiCertCA.crt
├── crls
│   └── ibm-z-host-key-gen2.crl
│   └── DigiCertTrustedRootG4.crl
│   └── DigiCertTrustedG4CodeSigningRSA4096SHA3842021CA1.crl
├── hdr
│   └── hdr.bin
├── hkds
│   └── HKD-3931-0275D38.crt
└── rsa
    ├── encrypt_key.pem
    └── encrypt_key.pub