packaging: setup: don't ask about cdrom using answer file

Previously if the cdrom was passed using answer file
the value was used as default for the question
about which image to use.
Now it's used as is without asking anything else
in non interactive mode.

Change-Id: Idf4e2e46d63f876c1988238ad3d22e560c1c2fc4
Signed-off-by: Sandro Bonazzola <sbonazzo@redhat.com>