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: I2702b6063bbee3e8de046b50998dcb17d1a7dad6
Merge "Create a new answer file when running on interactive mode"