packaging: setup: write answer file also on error

previously answer file was not written if an error occurred
at customization or if user did not accept configuration preview.
Also the answer file was not updated with late values asked at
closeup stage if an error occurred in that stage.
Now the answer file is always written.

Change-Id: Icf991ffaa44fbb16c7a97c76b9a4e17397aacaca
Bug-Url: https://bugzilla.redhat.com/1107772
Signed-off-by: Sandro Bonazzola <sbonazzo@redhat.com>