Refactor TunnelHolder so that is serializable again.  Introduced a (Serializable) TunnelManagerFactory that can be used to create the appropriate AbstractSauceTunnelManager on the slave node, when needed.
Merge branch 'TRE-2149-sfly-1.X-simplify-use-of-identified-tunnels' into sfly-1.X

Improve Serializability of components.