packaging: setup: added FQDN validation to engine-setup-2

- Added missing FQDN falidation to engine-setup-2
- Reverse lookup validation is done only if AIO is used.

Change-Id: Ie9764f32ba5e30062532bf11c67756677333c44f
Signed-off-by: Sandro Bonazzola <sbonazzo@redhat.com>