Gather facts in set_hostname playbook

The set_hostname playbook, used by the launch-node script, needs
facts to determine which package manager it should use to uninstall
cloud-init. Remove the line which disabled fact gathering so that we
can build servers again.

Change-Id: Ic971d456f6d04273c9b981518614130e9b1c5898

playbooks/set_hostnames.yml

@@ -1,7 +1,6 @@
 ---
 # file: set_hostnames.yml
 - hosts: "{{ target }}"
-  gather_facts: no
   user: root
   roles:
     - { role: set_hostname }