Match real and ansible hostnames when bootstrapping fresh EC2 instances.

This changed the box hostnames from e.g. ip-<private-ip> to hslave01. Other
roles and plays seem to assume this is how things are set-up anyway, which is
not true of bog-standard machines from EC2.

Ansible v1.4 now required, since I use the new ‘hostname’ action.
Merge pull request #3 from amirhhz/match-hostnames

Match real and ansible hostnames when bootstrapping fresh EC2 instances.