fix error in evaluation of when-condition

[FloRinke]

When running this role on a system with dhcp_mode=relay, execution fails:

TASK [debops.dhcpd : Convert list of nameservers to Ansible list] ********************************************************************************************
fatal: [router]: FAILED! => {"failed": true, "msg": "The conditional check '(dhcpd_register_nameservers is defined and dhcpd_register_nameservers.stdout)' failed. The error was: error while evaluating conditional ((dhcpd_register_nameservers is defined and dhcpd_register_nameservers.stdout and dhcpd_mode == 'server')): 'dict object' has no attribute 'stdout'\n\nThe error appears to have been in '/home/flo/.local/share/debops/debops-playbooks/roles/debops.dhcpd/tasks/main.yml': line 13, column 3, but may\nbe elsewhere in the file depending on the exact syntax problem.\n\nThe offending line appears to be:\n\n\n- name: Convert list of nameservers to Ansible list\n  ^ here\n"}

dhcpd_register_nameservers wasn't registered, because the previous task is only run when dhcpd_mode == 'server'. Apparently both conditions are being checked, even though the result was clear after the first one.

This can be solved by supplying an empty default for the non-defined variable.

(Happens with ansible 2.4.1.0)

[drybjed]

Sounds good. However, can you create a PR against the debops/debops repository instead? The code will be exported from there at some point.

[FloRinke]

sure, that can be arranged