Refactor properties to distinguish between node name and id

The helper functions used by the framework have different input
requirements.  Some that use rpc require the actual node name which
may be different depending on the harness used. Others use the node
identifier to form strings representing shell commands to execute. The
node property has been replaced by a node_id property and a node_map
structure that maps a node identifier to a full node name.
Update to rebar 2.5.1