Create a new answer file when running on interactive mode

In order to be able to run packstack again with the same config when
using it in interactive mode, packstack now creates an answer file right
after the paramteres are confirmed.

Fixes https://bugzilla.redhat.com/show_bug.cgi?id=906410

Change-Id: Id4cf4050be778077d56ea1f41ec8d113f840dbc2
Merge "Create a new answer file when running on interactive mode" into folsom