Moving inputs between cluster nodes does not start them

If you configure an existing input to a different node in the cluster,
it will get terminated on the old node, but not automatically started on the new cluster node.

## Expected Behavior
It should autmatically start the input on the new node.

## Steps to Reproduce (for bugs)
1. configure an input to cluster node A
2. observe that it's running
3. change the input config to cluster node B

* Graylog Version: 3.0 rc1