Remove all rte_panic() calls

Gatekeeper deployers have been increasing their reliance on Gatekeeper and Grantor servers. And, in these production environments, turning a disruptive failure into a graceful failure is a justifiable effort given the stakes. While moving toward higher standards is going to be a common theme in the evolution of Gatekeeper, it's certainly time to remove all `rte_panic()` calls present in the code.