Close deployment when all entities are done

[andreiolaru-ro]

Use a switch to turn this on or off - sometimes we need the system even if no entities run on it [anymore].

• [x] Decide which entities to monitor in order to decide system exit, as a general rule.
• [x] Change test scenarios to only do pings a limited number of times (e.g. 5 for simple scenarios, 10 for more complex), such that system exit is also tested.

[andreiolaru-ro]

Almost solved in commit f3fd5ec42bebe6c4d5b06a1e8969419e6b90391e.

• [ ] must still see how to do it when complex monitoring (MonitoringEntity, Web server) is involved.

[andreiolaru-ro]

• [ ] add relevant information in running.md
• [ ] check if information in deployment.md is still entirely valid