Allow creating cluster wide tasks

[adejanovski]

Fixes #25

[burmanm]

Why is this exported? Also, instead of modifying each task, would it have made more sense to modify the "CreateClusterTask()" function instead to modify this part:

	if len(datacenters) > 0 {
		task.Spec.Datacenters = datacenters
	}

To something like

	if len(datacenters) > 0 && datacenters[0] != "" {
		task.Spec.Datacenters = datacenters
	}

?

[adejanovski]

Why is this exported?

For testing purposes.

Also, instead of modifying each task, would it have made more sense to modify the "CreateClusterTask()" function instead to modify this part:

Done