packaging: setup: handle answerfile correctly

Previously if CREATE_READONLY_USER was specified
in answer file, the readonly user was not created.

Now if CREATE_READONLY_USER is set to yes or true
it will be created using validated values from:
- READONLY_SECURE
- READONLY_USER
- READONLY_PASS

Change-Id: I1598f4bfaf82b1713f6b0e4ee5b61d1053542702
Bug-Url: https://bugzilla.redhat.com/1040029
Signed-off-by: Sandro Bonazzola <sbonazzo@redhat.com>