When ansible do not load the file host_vars/{{ ansible_hostname }}.yml and host_vars/default.yml it will show syntactic err, so add keyword "skip" to fix it.
Exit the playbook if the user not define devices in both host_vars/{{ ansible_hostname }}.yml and host_vars/default.yml
host_vars/default.yml
load device partition file in directory host_vars
1) if the user define host_vars/hostname.yml load the devices partition on this file.
2) otherwise load host_vars/default.yml for default