Arvados

When the request queue of a Go service is over 90% busy, it should dump a list of outstanding requests to a file named something like:

<service>-request-queue.json

It should do this once per minute as long as the queue is over 90% busy.

This is enabled by a new configuration option that tells the services where to put their request queue files. The directory must be writable. If no value is set, don't do anything. If the directory does not exist or is not writable, log an (warning|error).