sc-hsm: Improve error detection and reporting in sc-hsm-tool
sc-hsm: Added error if private key import tried

Private key import is not supported by the SmartCard-HSM. However there is no error code
if it is still tried using pkcs15-init or from within Firefox.
sc-hsm: Fix certificate delete bug

If a certificate is deleted after the related private key, then the driver
picks the wrong certificate EF, leading to an CKR_GENERAL_ERROR or the wrong
certificate being deleted.