to make it easier/less disruptive to add nodes to a running cluster

to make it easier/less disruptive to add nodes to a running cluster

add a new control that causes the node to drop the current nodes list
and reread it from the nodes file.
During this operation, the node will also drop the tcp layer and restart it.

When we drop the tcp layer, by talloc_free()ing the ctcp structure
add a destructor to ctcp so that we also can clean up and remove the references in the ctdb structure to the transport layer

add two new commands for the ctdb tool.
one to list all nodes in the nodesfile and the second a command to trigger a node to drop the transport and reinitialize it with the nde nodes file