Add the new hostname to /etc/hosts in prepare_node

It is good practice to update /etc/hosts with the new hostname when
changing it. Some programs (such as sudo) will give warnings if it is
unable to resolve its own name.

Change-Id: I5c95c9cadc32d7d42c6c6546e136a80f4a7e02f4
Merge "Add the new hostname to /etc/hosts in prepare_node"