Reduce the time taken to identify an agent is offline

Problem

When an agent crashes or manually shut down, the Bamboo server will take about 10min to show the agent as offline. This time creates confusing to admins when managing their agents.

Solution suggested

Implement a mechanism where this time could be reduced and as soon the agent process is down the server would know about it.

Please consider an immediate server update also for the case when the agent is gracefully shutdown. The agent could notify the server changing the agent status to offline right away.