ksck's checksumming routine times out after 1 hour, by default, but I've seen that be too short a time. We can bump the timeout, but to find out if a timeout is too short you have to hit it, then restart the whole checksum, or manually figure out with tablets still need to be checksummed. We should allow the checksum to continue as long as it periodically makes progress.
Probably also need to address
KUDU-2179 for this to be helpful.