Also removes the conditional for skipping installation based on ansible_local.zerotier value. Skipping tasks like that should be up to the user, not the role.
Create /etc/ansible/facts.d/zerotier.fact on each node containing custom facts in json format. This can then be used to prevent pointless reconfiguration of existing nodes whenever a new one is added to the inventory. In this commit it merely skips the installation tasks.
Marcus Meurs