CE-2893: Allow both inventories and extra vars
This will go together with changes to the playbook in ics-ans-ioc, which
will do the work of determining whether or not we should use the inventory
or the extra vars. In this case, it seems simpler to have ics-ans-role-ioc
only care about iocs_to_(un)deploy
.
Note further that defaults are provided so there is not a need to pipe them through a default.