Rudder

When you configure the scheduling for the system updrage technique, there is several suprising things:

- campaign duration is actually a spread, but there is no information on that. We need to add some something saying "Nodes update will be randomly spread on that interval, starting at scheduled date"
- it's strange to have the spread part before the scheduling part, that should be inverted
- the schedule is based on UTC, which is good, but surprising as it's not said. We need to add "(UTC)" next to Hours field