Fix node ping interval code / default setting code

Change the place where we set the defaults for node ping
and node status interval. This problem manifested itself
by the node ping interval being 0 when it was set to
the default.

This makes two changes:
1. Invalid ping values, and ping timeouts will not
   allow VK to start up
2. We set the default values very early on in creation
   of the node controller -- where all the other values
   are set.

Signed-off-by: Sargun Dhillon <sargun@sargun.me>

node/node_ping_controller.go

@@ -28,6 +28,14 @@ type pingResult struct {
 }
 
 func newNodePingController(node NodeProvider, pingInterval time.Duration, timeout *time.Duration) *nodePingController {
+	if pingInterval == 0 {
+		panic("Node ping interval is 0")
+	}
+
+	if timeout != nil && *timeout == 0 {
+		panic("Node ping timeout is 0")
+	}
+
 	return &nodePingController{
 		nodeProvider:       node,
 		pingInterval:       pingInterval,