Unable to view queues after loss of build agent

When a build agent goes down unexpectedly, the system does not handle it gracefully.

The Queues page (/displayQueues!display.action) shows Error Occurred org.apache.maven.continuum.ContinuumException: Error retrieving projects currently preparing build in http://localhost:8181/continuum-buildagent/xmlrpc

To reproduce, add 2 or more agents, force a bunch of builds, then stop one of the agents without disabling it from the master.

I notice that the Build Agents page (/buildAgentList.action) still shows the agent as Enabled=true, even though it is not responding.

There should probably be some concept of the system automatically disabling an agent that is not behaving correctly. For now I'd be happy with the admin having to manually re-enable it, but an auto-recovery feature might be a nice enhancement for later.