reorg: simplifies packstack roles

- moves all answer_file generation to a simple role: generate answers
- deletes packstack-neutron-aio, nova-aio, quantum-aio, rhos/epel roles as
  they are replaced by ksgen settings files
- multinode role now generates the packstack answer for aio and multinode jobs

Change-Id: I6d07788cd68395826efc00fe2fcb119c83c2b9aa