Capture agent with no configuration is always shown as "idle"

Steps to reproduce:
1. Use REST endpoint to register a new capture agent as idle
2. Send no additional communication from agent.
3. View "Capture Agents" tab on admin UI

Actual Results:
Capture Agent shows up as "idle" indefinitely

Expected Results:
Capture agent should eventually appear as offline

Workaround (if any):
Send a configuration