hbacrule: Create FQDN from single hostnames

Single hostnames can be used for hbacrule_add_host and will match fqdn
in IPA internally. Simple host names have to be extended to be FQDN to
be able to compare them for _host_add and _host_remove.

Two new functions have been added to ansible_freeipa_module:

- api_get_domain - Get the domain from the api
- ensure_fqdn - Extend a single name with the domain

This fixes #617 - hbacrule_add_host: already a member