Attestation monitoring bypass via silent task termination

Uncaught exceptions in Keylime before 6.5.1 allow attackers controlling an agent to halt verifier checks while it remains attested. The asynchronous request wrapper in keylime/tornado_requests.py catches only several expected exception types and returns None for an empty response, so other transport failures escape or violate caller expectations and terminate polling without a database record or log entry. A rogue or failing agent must cause a transient network or recoverable device-driver failure path; only that agent's ongoing attestation is interrupted while its prior trusted state remains visible.