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
Create a cinder volume if it doesn't exists

This patch adds support for volume group creation. Since we're not able
to change cinder's volume name in cinder's confgs (yet), we'll be
prompting the user just for the volume's path and size

Change-Id: Idd799b2ba6ab2ba48fd8acd4228735747ae0ebee
Merge "Create a new answer file when running on interactive mode"