Get ride of most static covers in RequestFilter

This makes it easier to test as we can just mock the ComponentManager and use that to get our services.
Add test of the RequestFilter.assureSession()
WL-3014 Allow nodes to be marked as handling no new sessions.

The cluster service now has a status and nodes in the cluster can request that a node change status. Once a node is halting it doesn’t handle any new sessions but will continue to service existing ones.
Merge pull request #52 from ox-it/WL-3014

WL-3014 Allow new sessions to stop hitting node.