Audit Failure Semantics

This is needed for FISMA, and several other compliance regulations.

Failure semantics means when auditing fails (the ability to retry and configure retry, the ability to block transactions, or shutdown server, or continue )

currently the behaviour is continue even if audit cannot be written.

 
Similar to the option added to auto-failover if disk writes are failing, we need to add an option to automatically failover a node when Couchbase Server Auditing fails to record an audit record.  The node should also fail to start-up if auditing is malfunctioning.